Incorrect handling of svn:mergeinfo during merging on the svnpatch-diff branch

I discovered 2 bugs in handling of svn:mergeinfo when I was performing some
merges on the svnpatch-diff branch.

1. Addition of incorrect svn:mergeinfo on some files or directories:

Steps to reproduce:
 svn co -r32624 https://svn.collab.net/repos/svn/branches/svnpatch-diff subversion-svnpatch-diff-r32624
 cd subversion-svnpatch-diff-r32624
 svn merge -r32500:32620 ^/trunk

This merge adds incorrect svn:mergeinfo on:
 build.conf
 subversion/include
 subversion/libsvn_subr
 subversion/tests/libsvn_subr

These files / directories don't have svn:mergeinfo before merging.
After merging, svn:mergeinfo on these files / directories doesn't contain:
 /trunk:1-31375,31378-32620

(Next `svn merge ^/trunk` would try to merge r25664:30782 from trunk which causes
many conflicts.)

2. Incomplete reversion of changes during reverse merging:

Steps to reproduce:
 svn co -r32625 https://svn.collab.net/repos/svn/branches/svnpatch-diff subversion-svnpatch-diff-r32625
 cd subversion-svnpatch-diff-r32625
 svn merge -c-32625 ^/branches/svnpatch-diff

r32625 added (incorrect) svn:mergeinfo on:
 build.conf
 subversion/include
 subversion/libsvn_subr
 subversion/tests/libsvn_subr

Reverse merging should delete svn:mergeinfo property, but it leaves empty svn:mergeinfo.

-- 
Arfrever Frehtes Taifersar Arahesis