Merge branch 'ma/unpack-trees-free-msgs'

Leak plugging.

* ma/unpack-trees-free-msgs:
unpack_trees_options: free messages when done
argv-array: return the pushed string from argv_push*()
merge-recursive: provide pair of `unpack_trees_{start,finish}()`
merge: setup `opts` later in `checkout_fast_forward()`

diff --cc argv-array.c
Simple merge

diff --cc argv-array.h
Simple merge

diff --cc builtin/checkout.c
Simple merge

diff --cc merge-recursive.c
Simple merge

diff --cc merge.c
Simple merge

diff --cc unpack-trees.c
Simple merge