Merge branch 'jk/parse-commit-with-malformed-ident'

Merge branch 'jk/parse-commit-with-malformed-ident'

The commit object parser has been taught to be a bit more lenient
to parse timestamps on the author/committer line with a malformed
author/committer ident.

* jk/parse-commit-with-malformed-ident:
  parse_commit(): describe more date-parsing failure modes
  parse_commit(): handle broken whitespace-only timestamp
  parse_commit(): parse timestamp from end of line
  t4212: avoid putting git on left-hand side of pipe