On the 1.9.x-strict-rep-sharing branch, merge r1794611, resolving conflicts.

Changes to subversion/libsvn_fs_x/transaction.c were discarded since there
is no need to backport fixes for FSX (and the change conflicted anyway).

The error code SVN_ERR_FS_AMBIGUOUS_CHECKSUM_REP does not exist in 1.9.x
so SVN_ERR_FS_GENERAL was used instead, as was done in earlier commits to
this branch.


git-svn-id: https://svn.apache.org/repos/asf/subversion/branches/1.9.x-strict-rep-sharing@1794613 13f79535-47bb-0310-9956-ffa450edef68