Brad King authored Oct 13, 2011 and Junio C Hamano committed Oct 13, 2011

The submodule merge search is not useful during virtual merges because
the results cannot be used automatically.  Furthermore any suggestions
made by the search may apply to commits different than HEAD:sub and
MERGE_HEAD:sub, thus confusing the user.  Skip searching for submodule
merges during a virtual merge such as that between B and C while merging
the heads of:

    B---BC
   / \ /
  A   X
   \ / \
    C---CB

Run the search only when the recursion level is zero (!o->call_depth).
This fixes known breakage tested in t7405-submodule-merge.

Signed-off-by: Brad King <brad.king@kitware.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>