Fix XML-escaping in mergeinfo request.
Fix XML-escaping in mergeinfo request.

* subversion/libsvn_ra_serf/mergeinfo.c
  (create_mergeinfo_body): Do not escape tag body twice. 
   svn_ra_serf__add_tag_buckets() already escapes tag body.

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