Make svn_client_patch() enforce that the patch source is an existing file.
Make svn_client_patch() enforce that the patch source is an existing file.

* subversion/libsvn_client/patch.c
  (svn_client_patch): Provide reasonable error messages when the patch
   does not exist or is not a file. While here fix stray whitespace.

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