Followup to r27875. Add logic to tell whether the path being diffed is the

Followup to r27875.  Add logic to tell whether the path being diffed is the
same as the path the diff paths should be relative to.  In that scenario,
specify a path of '.' in the diff output, instead of throwing an error.

* subversion/libsvn_client/diff.c:
  (display_prop_diffs, diff_content_changed): Updated for new path check.

[ in subversion/bindings/javahl/ ]

* tests/org/tigris/subversion/javahl/BasicTests.java
  (testDiff): Test scenario where path and relative path are the same.

Patch by: Jeremy Whitlock <jwhitlock@collab.net>

git-svn-id: http://svn.collab.net/repos/svn/trunk@28374 612f8ebc-c883-4be0-9ee0-a4e9ef946e3a