git-p4: format-patch to diff-tree change breaks binary patches

When applying binary patches a full index is required. format-patch
already handles this, but diff-tree needs '--full-index' argument
to always output full index. When git-p4 runs git-apply to test
the patch, git-apply rejects the patch due to abbreviated blob
object names. This is the error message git-apply emits in this
case:

    error: cannot apply binary patch to '<filename>' without full index line
    error: <filename>: patch does not apply

Signed-off-by: Tolga Ceylan <tolga.ceylan@gmail.com>
Acked-by: Pete Wyckoff <pw@padd.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>