Merge branch 'jk/ident-gecos-strbuf'

Fixes quite a lot of brokenness when ident information needs to be taken
from the system and cleans up the code.

By Jeff King
* jk/ident-gecos-strbuf: (22 commits)
  format-patch: do not use bogus email addresses in message ids
  ident: reject bogus email addresses with IDENT_STRICT
  ident: rename IDENT_ERROR_ON_NO_NAME to IDENT_STRICT
  format-patch: use GIT_COMMITTER_EMAIL in message ids
  ident: let callers omit name with fmt_indent
  ident: refactor NO_DATE flag in fmt_ident
  ident: reword empty ident error message
  format-patch: refactor get_patch_filename
  ident: trim whitespace from default name/email
  ident: use a dynamic strbuf in fmt_ident
  ident: use full dns names to generate email addresses
  ident: report passwd errors with a more friendly message
  drop length limitations on gecos-derived names and emails
  ident: don't write fallback username into git_default_name
  fmt_ident: drop IDENT_WARN_ON_NO_NAME code
  format-patch: use default email for generating message ids
  ident: trim trailing newline from /etc/mailname
  move git_default_* variables to ident.c
  move identity config parsing to ident.c
  fmt-merge-msg: don't use static buffer in record_person
  ...

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

diff --cc cache.h
Simple merge

diff --cc ident.c
Simple merge