merge-recursive: Fix virtual merge base for rename/rename(1to2)/add-dest

merge-recursive: Fix virtual merge base for rename/rename(1to2)/add-dest

Earlier in this series, the patch "merge-recursive: add handling for
rename/rename/add-dest/add-dest" added code to handle the rename on each
side of history also being involved in a rename/add conflict, but only
did so in the non-recursive case.  Add code for the recursive case,
ensuring that the "added" files are not simply deleted.

Signed-off-by: Elijah Newren <newren@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>