cg-update (cogito-0.13) bug: changed heads

I just found a bug in cogito-0.13, at least to the best of my 
understanding of the situation.

Simplified, the problem looks like this: two sides, A and B, pull from 
repository C.  The head of this pull we call 0.

Now commit 1 is added to A.  B pulls commit 1 from A, not though C. 
Later, A pushes commit 1 to C.

Next time B tries to pull from C, cg-update will not advance 
refs/heads/origin, even though C now has a new head.  Thus, B will think 
that C is in a different state than it actually is.

This has, for me, broken safeguards of the form "make sure you're merged 
before you pull."

	-hpa