Confluence should explicitly check for other confluence instances using the same home directory

If two Confluence instances are run against the same home directory then they will cluster-panic and die. This is confusing for users who know that they don't have a cluster. Other Atlassian products (eg JIRA) that don't have clustering, place a lock on the home directory to more clearly show what is going on in this instance. It would be great for Confluence to do this too.

Although there is currently some unpleasantness around having to frequently remove lock files by hand after JIRA dies, I gather these are soon to be solved.