fsck: fix bogus commit header check

fsck: fix bogus commit header check

daae1922 (fsck: check ident lines in commit objects, 2010-04-24)
taught fsck to expect commit objects to have the form

  tree <object name>
  <parents>
  author <valid ident string>
  committer <valid ident string>

  log message

The check is overly strict: for example, it errors out with the
message “expected blank line” for perfectly valid commits with an
"encoding ISO-8859-1" line.

Later it might make sense to teach fsck about the rest of the header
and warn about unrecognized header lines, but for simplicity, let’s
accept arbitrary trailing lines for now.

Reported-by: Tuncer Ayaz <tuncer.ayaz@gmail.com>
Signed-off-by: Jonathan Nieder <jrnieder@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>