Include checkpoint command in the BNF.
Include checkpoint command in the BNF.

This command isn't encouraged (as its slow) but it does exist and
is accepted, so it still should be covered in the BNF.

Signed-off-by: Shawn O. Pearce <f01032651c12a22b2103346ba96b3b6b231f9d3c@spearce.org>

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