[PATCH 0/7] cleaning up determine_author_info

This is another function I ran across in today's cleanups. The memory
leak in it has bugged me for a while (even though it's really not a big
deal in practice). So this is mostly minor cleanups, but I did find a
bug in the commit parser.

  [1/7]: commit: provide a function to find a header in a buffer
  [2/7]: record_author_info: fix memory leak on malformed commit
  [3/7]: record_author_info: use find_commit_header
  [4/7]: ident_split: store begin/end pairs on their own struct
  [5/7]: use strbufs in date functions
  [6/7]: determine_author_info: reuse parsing functions
  [7/7]: determine_author_info: stop leaking name/email

I built it on top of my commit-slab topic, as otherwise you get some
textual conflicts in determine_author_info. But I notice that Junio's
jk/commit-buffer-length is based on an older master; applying there
produces some other minor textual conflicts. I can build it on whatever
is convenient and handle the conflicts myself. But if
jk/commit-buffer-length is set to graduate soon (as it is marked in WC),
I can just hold onto this until then.

-Peff