Using it in the first place means something's wrong.
This patch replaces it with an internal header which
carries the previously "protected" code instead.

Internal source-files simply include "commit.h" and
they're done. The internal header includes the public
one to make sure we always use the proper prototype.

Signed-off-by: Andreas Ericsson <ae@op5.se>
Signed-off-by: Shawn O. Pearce <spearce@spearce.org>