t5520: verify that `pull --rebase` shows the helpful advice when failing
It was noticed by Brendan Forster last October that the builtin `git am`
regressed on that. Our hot fix reverted to spawning the recursive merge
instead of using it as a library function.
As we are about to revert that hot fix, after making the recursive merge a
true library function (i.e. a function that does not die() in case of
"normal" errors), let's add a test that verifies that we do not regress on
the same problem which made the hot fix necessary in the first place.
Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
Signed-off-by: Junio C Hamano <gitster@pobox.com>