Merge branch 'jk/reset-ident-time-per-commit' into maint

Merge branch 'jk/reset-ident-time-per-commit' into maint

Not-so-recent rewrite of "git am" that started making internal
calls into the commit machinery had an unintended regression, in
that no matter how many seconds it took to apply many patches, the
resulting committer timestamp for the resulting commits were all
the same.

* jk/reset-ident-time-per-commit:
  am: reset cached ident date for each patch