Simon Heimberg <simohe@besonet.ch> [Thu, 14 May 2009 19:54:26 +0200] rev 8589
dirstate: skip step 3 in walk if nothing new will match
nothing will ever match on match.never
nothing new will match on match.exact (all found in step 1)
nothing new will match on match.match when
there is no pattern and
there is no direcory in pats