Merge branch 'ma/reduce-heads-leakfix'

Leak fixes.

* ma/reduce-heads-leakfix:
  reduce_heads: fix memory leaks
  builtin/merge-base: free commit lists

diff --cc builtin/commit.c
Simple merge

diff --cc builtin/fmt-merge-msg.c
Simple merge

diff --cc builtin/merge-base.c
Simple merge

diff --cc builtin/merge.c
Simple merge

diff --cc builtin/pull.c
Simple merge