Unable to edit channel properties when site runs under a context path

When a channel is saved, the full URL path of the channel is used to locate the mount of the channel. This is not correct when the URL path contains a context path (e.g. '/site').

Steps to reproduce:
1. start the archetype on localhost (e.g. the testsuite or archetype)
2. open a channel in the template composer
3. open the 'channel settings' box
4. edit a channel property and click 'Save'

Expected behavior: the channel property is saved
Actual behavior: the following stacktrace is logged:

[INFO] [talledLocalContainer] 12.12.2011 12:15:34 ERROR [org.onehippo.cms7.channelmanager.channels.ChannelPropertiesWindow.save():260] Could not save channel
[INFO] [talledLocalContainer] org.hippoecm.hst.configuration.channel.MountNotFoundException: /hst:hst/hst:hosts/dev-localhost/localhost/hst:root/site
[INFO] [talledLocalContainer] at org.hippoecm.hst.configuration.channel.ChannelManagerImpl.updateChannel(ChannelManagerImpl.java:720)
[INFO] [talledLocalContainer] at org.hippoecm.hst.configuration.channel.ChannelManagerImpl.save(ChannelManagerImpl.java:404)
[INFO] [talledLocalContainer] at org.onehippo.cms7.channelmanager.channels.ChannelPropertiesWindow$5.run(ChannelPropertiesWindow.java:255)
[INFO] [talledLocalContainer] at org.onehippo.cms7.channelmanager.channels.ChannelPropertiesWindow$5.run(ChannelPropertiesWindow.java:253)
[INFO] [talledLocalContainer] at java.security.AccessController.doPrivileged(Native Method)
[INFO] [talledLocalContainer] at javax.security.auth.Subject.doAsPrivileged(Subject.java:517)
[INFO] [talledLocalContainer] at org.hippoecm.hst.security.HstSubject.doAsPrivileged(HstSubject.java:117)
[INFO] [talledLocalContainer] at org.onehippo.cms7.channelmanager.channels.ChannelPropertiesWindow.save(ChannelPropertiesWindow.java:253)
[INFO] [talledLocalContainer] at org.onehippo.cms7.channelmanager.channels.ChannelPropertiesWindow.access$500(ChannelPropertiesWindow.java:73)
[INFO] [talledLocalContainer] at org.onehippo.cms7.channelmanager.channels.ChannelPropertiesWindow$4.onEvent(ChannelPropertiesWindow.java:230)
[INFO] [talledLocalContainer] at org.wicketstuff.js.ext.ExtEventAjaxBehavior.handle(ExtEventAjaxBehavior.java:91)
[INFO] [talledLocalContainer] at org.wicketstuff.js.ext.ExtEventAjaxBehavior.respond(ExtEventAjaxBehavior.java:55)
[INFO] [talledLocalContainer] at org.apache.wicket.ajax.AbstractDefaultAjaxBehavior.onRequest(AbstractDefaultAjaxBehavior.java:302)
[INFO] [talledLocalContainer] at org.apache.wicket.request.target.component.listener.BehaviorRequestTarget.processEvents(BehaviorRequestTarget.java:157)
[INFO] [talledLocalContainer] at org.apache.wicket.request.AbstractRequestCycleProcessor.processEvents(AbstractRequestCycleProcessor.java:92)
[INFO] [talledLocalContainer] at org.hippoecm.frontend.PluginRequestCycleProcessor.processEvents(PluginRequestCycleProcessor.java:95)
[INFO] [talledLocalContainer] at org.apache.wicket.RequestCycle.processEventsAndRespond(RequestCycle.java:1252)
[INFO] [talledLocalContainer] at org.apache.wicket.RequestCycle.step(RequestCycle.java:1331)
[INFO] [talledLocalContainer] at org.apache.wicket.RequestCycle.steps(RequestCycle.java:1438)
[INFO] [talledLocalContainer] at org.apache.wicket.RequestCycle.request(RequestCycle.java:546)
[INFO] [talledLocalContainer] at org.apache.wicket.protocol.http.WicketFilter.doGet(WicketFilter.java:486)
[INFO] [talledLocalContainer] at org.apache.wicket.protocol.http.WicketFilter.doFilter(WicketFilter.java:319)
[INFO] [talledLocalContainer] at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:235)
[INFO] [talledLocalContainer] at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206)
[INFO] [talledLocalContainer] at org.hippoecm.frontend.ResourceRewriteFilter.doFilter(ResourceRewriteFilter.java:129)
[INFO] [talledLocalContainer] at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:235)
[INFO] [talledLocalContainer] at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206)
[INFO] [talledLocalContainer] at org.hippoecm.frontend.plugins.login.ConcurrentLoginFilter.doFilter(ConcurrentLoginFilter.java:54)
[INFO] [talledLocalContainer] at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:235)
[INFO] [talledLocalContainer] at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206)
[INFO] [talledLocalContainer] at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:233)
[INFO] [talledLocalContainer] at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:191)
[INFO] [talledLocalContainer] at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:127)
[INFO] [talledLocalContainer] at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:102)
[INFO] [talledLocalContainer] at org.apache.catalina.valves.AccessLogValve.invoke(AccessLogValve.java:589)
[INFO] [talledLocalContainer] at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:109)
[INFO] [talledLocalContainer] at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:291)
[INFO] [talledLocalContainer] at org.apache.coyote.http11.Http11Processor.process(Http11Processor.java:859)
[INFO] [talledLocalContainer] at org.apache.coyote.http11.Http11Protocol$Http11ConnectionHandler.process(Http11Protocol.java:602)
[INFO] [talledLocalContainer] at org.apache.tomcat.util.net.JIoEndpoint$Worker.run(JIoEndpoint.java:489)
[INFO] [talledLocalContainer] at java.lang.Thread.run(Thread.java:662)