Merge branch 'jc/mailinfo-lib'

Merge branch 'jc/mailinfo-lib'

The implementation of "git mailinfo" was refactored so that a
mailinfo() function can be directly called from inside a process.

* jc/mailinfo-lib: (34 commits)
  mailinfo: remove calls to exit() and die() deep in the callchain
  mailinfo: handle charset conversion errors in the caller
  mailinfo: libify
  mailinfo: keep the parsed log message in a strbuf
  mailinfo: handle_commit_msg() shouldn't be called after finding patchbreak
  mailinfo: move content/content_top to struct mailinfo
  mailinfo: move [ps]_hdr_data to struct mailinfo
  mailinfo: move cmitmsg and patchfile to struct mailinfo
  mailinfo: move charset to struct mailinfo
  mailinfo: move transfer_encoding to struct mailinfo
  mailinfo: move check for metainfo_charset to convert_to_utf8()
  mailinfo: move metainfo_charset to struct mailinfo
  mailinfo: move use_scissors and use_inbody_headers to struct mailinfo
  mailinfo: move add_message_id and message_id to struct mailinfo
  mailinfo: move patch_lines to struct mailinfo
  mailinfo: move filter/header stage to struct mailinfo
  mailinfo: move global "FILE *fin, *fout" to struct mailinfo
  mailinfo: move keep_subject & keep_non_patch_bracket to struct mailinfo
  mailinfo: introduce "struct mailinfo" to hold globals
  mailinfo: move global "line" into mailinfo() function
  ...