When two different files are renamed to one, we need to be able to do
three-way merges for both of those files. To do that, we need to record
the sha1sum of the (possibly modified) file on the unrenamed side. Modify
setup_rename_conflict_info() to take this extra information and record it
when the rename_type is RENAME_TWO_FILES_TO_ONE.
Signed-off-by: Elijah Newren <newren@gmail.com> Signed-off-by: Junio C Hamano <gitster@pobox.com>