Revert the move of lost_context setting to UNLOCK_HARDWARE that was done in the

Revert the move of lost_context setting to UNLOCK_HARDWARE that was done in the
last commit.  I've been convinced by keithw that it's sufficient, and put a note
in the code about it.

Close another race for state in the Clear functions.  I made the situation worse
in my last commit, but this should fix things.  Might be a slight performance
hit, which could be regained by splitting the R*_FIREVERTICES calls in r*Clear
up so that the EmitState doesn't happen in a separate new cmdbuf.