Really fix my ifdef-d-out mergeinfo repair/migration svnsync logic to account for the way svnmerge really stores its data?  (Follow-up to r29643.)
Really fix my ifdef-d-out mergeinfo repair/migration svnsync logic to account
for the way svnmerge really stores its data?  (Follow-up to r29643.)

* subversion/svnsync/main.c
  (change_dir_prop): Use a stringbuf to build the mergeinfo string in
    pieces, which allows me to do what I *meant* to do before in this
    code and omit blank lines and such which might live in the
    svnmerge property values.


git-svn-id: f8a4e5e023278da1e04e203c7fe051e3c4285d88@869718 13f79535-47bb-0310-9956-ffa450edef68

wbond/subversion,YueLinHo/Subversion,wbond/subversion,YueLinHo/Subversion,wbond/subversion,wbond/subversion,YueLinHo/Subversion,YueLinHo/Subversion,wbond/subversion,YueLinHo/Subversion,wbond/subversion,YueLinHo/Subversion,wbond/subversion,YueLinHo/Subversion,YueLinHo/Subversion