On the 'move-tracking-2' branch: Error rather than crash.
On the 'move-tracking-2' branch: Error rather than crash.

* subversion/libsvn_delta/branch.c
  (branch_state_alter): Return an error message rather than an assertion
    failure on some conditions which currently a merge can attempt to create.

git-svn-id: 486ec3464084f62cfe8608152673c827b947faa2@1711059 13f79535-47bb-0310-9956-ffa450edef68

YueLinHo/Subversion,YueLinHo/Subversion,YueLinHo/Subversion,YueLinHo/Subversion,YueLinHo/Subversion,YueLinHo/Subversion,YueLinHo/Subversion,YueLinHo/Subversion