Fix the '-rPREV' case when performing an export on a working copy.
Fix the '-rPREV' case when performing an export on a working copy.

* subversion/libsvn_client/export.c
  (svn_client_export): Stop clobbering from since we need it when trying to
  obtain a valid revnum when we need to contact the repository.  Also,
  svn_client__get_revision_number() needed the WC path, not where we're
  exporting to.

jmckaskill/subversion,jmckaskill/subversion,jmckaskill/subversion,jmckaskill/subversion,jmckaskill/subversion,jmckaskill/subversion,jmckaskill/subversion,jmckaskill/subversion