revert: fix parse_options_concat() leak

revert: fix parse_options_concat() leak

Free memory from parse_options_concat(), which comes from code
originally added (then extended) in [1].

At this point we could get several more tests leak-free by free()-ing
the xstrdup() just above the line being changed, but that one's
trickier than it seems. The sequencer_remove_state() function
supposedly owns it, but sometimes we don't call it. I have a fix for
it, but it's non-trivial, so let's fix the easy one first.

1. c62f6ec341b (revert: add --ff option to allow fast forward when
   cherry-picking, 2010-03-06)

Signed-off-by: Ævar Arnfjörð Bjarmason <avarab@gmail.com>
Signed-off-by: Taylor Blau <me@ttaylorr.com>