When filtering self-referential mergeinfo don't discard empty mergeinfo.
When filtering self-referential mergeinfo don't discard empty mergeinfo.

See http://subversion.tigris.org/servlets/ReadMsg?list=dev&msgNo=137120

* subversion/libsvn_client/merge.c
  (filter_self_referential_mergeinfo): Don't filter empty svn:mergeinfo.

Suggested by: kameshj

### THIS WAS REVERTED IN r30509 ###

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