Expose the 'diff_ignore_ancestry' option in the automatic merge API (which
is new since 1.7 so can be changed without deprecating).

* subversion/include/svn_client.h,
  subversion/libsvn_client/merge.c
  (svn_client_do_automatic_merge): Add a 'diff_ignore_ancestry' parameter.

* subversion/svn/merge-cmd.c
  (automatic_merge): Same, and pass it through.
  (svn_cl__merge): Pass FALSE for this new param to automatic_merge().


git-svn-id: https://svn.apache.org/repos/asf/subversion/trunk@1437097 13f79535-47bb-0310-9956-ffa450edef68