Flag another case of invalid merge input.
Flag another case of invalid merge input.

* subversion/svn/merge-cmd.c
  (svn_cl__merge): Move some input validation up a bit, and now check
    for folks trying to use --reintegrate with two merge sources, too.


git-svn-id: f8a4e5e023278da1e04e203c7fe051e3c4285d88@959004 13f79535-47bb-0310-9956-ffa450edef68

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