merge-recursive: fix logic ordering issue

merge-recursive: fix logic ordering issue

merge_trees() did a variety of work, including:
  * Calling get_unmerged() to get unmerged entries
  * Calling record_df_conflict_files() with all unmerged entries to
    do some work to ensure we could handle D/F conflicts correctly
  * Calling get_renames() to check for renames.

An easily overlooked issue is that get_renames() can create more
unmerged entries and add them to the list, which have the possibility of
being involved in D/F conflicts.  So the call to
record_df_conflict_files() should really be moved after all the rename
detection.  I didn't come up with any testcases demonstrating any bugs
with the old ordering, but I suspect there were some for both normal
renames and for directory renames.  Fix the ordering.

Reviewed-By: Stefan Beller <sbeller@google.com>
Signed-off-by: Elijah Newren <newren@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>