Validate POM SCM URL matches actual SCM URL used in the Add dialog

Added Commons Lang from here:

http://svn.apache.org/repos/asf/commons/proper/lang/trunk

Works OK, picks up version 3.0-SNAPSHOT

Now add Commons Lang from the following branch:

http://svn.apache.org/repos/asf/commons/proper/lang/branches/LANG_2_X

Appears to work OK, but the SCM is set to

scm:svn:http://svn.apache.org/repos/asf/commons/proper/lang/trunk

See: http://vmbuild.apache.org/continuum/projectView.action?projectId=135

The only way to fix this appears to be to edit the SCM URL, which should not be necessary.