Add some #ifdef-d-out logic for purging svn:mergeinfo and migrating

Add some #ifdef-d-out logic for purging svn:mergeinfo and migrating
svnmerge tracking data using svnsync.

* subversion/svnsync/main.c
  If SVN_SYNC__REPAIR_MERGEINFO is #defined...
  (change_file_prop): ...drop svn:mergeinfo properties and bogus
    (because they only apply to directories) svnmerge-integrated
    and svnmerge-blocked properties.
  (change_dir_prop): ...drop svn:mergeinfo properties, rename
    svnmerge-integrated properties to svn:mergeinfo, and warn about
    (but allow) svnmerge-blocked properties.

git-svn-id: http://svn.collab.net/repos/svn/trunk@29641 612f8ebc-c883-4be0-9ee0-a4e9ef946e3a