Merge branch 'jk/chopped-ident'

Merge branch 'jk/chopped-ident'

A commit object whose author or committer ident are malformed
crashed some code that trusted that a name, an email and an
timestamp can always be found in it.

* jk/chopped-ident:
  blame: handle broken commit headers gracefully
  pretty: handle broken commit headers gracefully
  cat-file: print tags raw for "cat-file -p"