Broken Links Checker: too much logging about invalid URL characters

Issue originally logged by Bart as HIPCON-916:

In the catalina.out repeatedly the following message is logged:
Exception in thread "Thread-61018" java.lang.IllegalArgumentException: Illegal character in path at index 34: http://issues.onehippo.com/browse/[HSTTWO-942]
at java.net.URI.create(URI.java:859)
at org.apache.http.client.methods.HttpHead.<init>(HttpHead.java:72)
at org.onehippo.cms7.brokenlinks.LinkChecker$LinkCheckerRunner.run(LinkChecker.java:150)
Caused by: java.net.URISyntaxException: Illegal character in path at index 34: http://issues.onehippo.com/browse/[HSTTWO-942]
at java.net.URI$Parser.fail(URI.java:2829)
at java.net.URI$Parser.checkChars(URI.java:3002)
at java.net.URI$Parser.parseHierarchical(URI.java:3086)
at java.net.URI$Parser.parse(URI.java:3034)
at java.net.URI.<init>(URI.java:595)
at java.net.URI.create(URI.java:857)
... 2 more

It shouldn't log an error, it shouldn't log in catalina.out and it shouldn't log it repeatedly. It should just mark the link as broken and be done with it.