Checks on folder nodes must also include directory node types

In at least one place (org.onehippo.cms.channelmanager.content.document.util.FolderUtils#nodeWithDisplayNameExists) the code checks if a jcr node represents a folder. Currently only a check on primary node type "hippostd:folder" is done. But a node of type "hippostd:directory" also represents a folder. Since the one type does not extend from the other, both checks need to be done explicity.

Please check the code base for more occurences.