t6422: fix multiple errors with the mod6 test expectations
This test had multiple issues causing it to fail for the wrong
reason(s):
* rename/rename(1to2) conflicts have always left the original source
path present in the working directory and index (at stage 1). Thus,
the triple rename/rename(1to2) should result in 9 unstaged files,
not 6.
* It messed up the three-way content merge for checking the results of
merging for one of the renames, accidentally turning it into a
two-way merge.
* It got the contents of the base files it was using to compare
against wrong, due to an off-by-one error, and overwrite-redirection
('>') instead of append-redirection ('>>').
* It used slightly too-long conflict markers
* It didn't include filenames in the conflict marker hunks (granted,
that was a shortcoming of the merge-recursive backend for rename/add
and rename/rename(2to1) conflicts, but since it's
test_expect_failure anyway we might as well make it expect our
preferred behavior rather than some compromise that we can't yet
reach anyway).
Fix these issues so that a merge backend which correctly handles these
kinds of nested conflicts will pass the test.
Signed-off-by: Elijah Newren <newren@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>