mailinfo: move check_header() after the helpers it uses
mailinfo: move check_header() after the helpers it uses

This way, we can lose a forward decl for decode_header().

Signed-off-by: Junio C Hamano <a6723cc3f76163bf7adb636a73ac3b0ceb3e6b9b@pobox.com>

destenson/git,destenson/git,destenson/git,destenson/git,destenson/git,destenson/git,destenson/git,destenson/git