Make all 'reintegrate' and 'sync' merges use the 'symmetric merge' code.

### This isn't quite ready to be committed; not all tests pass yet.

### Does this catch sync/reint merges where a maximum source revision
    is given? We should be able to use 'symmetric merge' for those.

* subversion/svn/merge-cmd.c
  (svn_cl__merge): Use the symmetric merge code for reintegrate and sync
   merges, as well as when the '--symmetric' option is given.
--This line, and those below, will be ignored--

Index: subversion/svn/merge-cmd.c
===================================================================
--- subversion/svn/merge-cmd.c	(revision 1342199)
+++ subversion/svn/merge-cmd.c	(working copy)
@@ -385,7 +385,14 @@ svn_cl__merge(apr_getopt_t *os,
     }
 
 #ifdef SVN_WITH_SYMMETRIC_MERGE
-  if (opt_state->symmetric_merge)
+  /* Do a symmetric merge if explicitly requested, or if a reintegrate
+   * is requested, or if a sync merge is requested by specifying just
+   * one source and no revisions. */
+  if (opt_state->symmetric_merge
+      || opt_state->reintegrate
+      || (! two_sources_specified
+          && first_range_start.kind == svn_opt_revision_unspecified
+          && first_range_end.kind == svn_opt_revision_unspecified))
     {
       svn_boolean_t allow_local_mods = ! opt_state->reintegrate;
       svn_boolean_t allow_switched_subtrees = ! opt_state->reintegrate;