[PATCH 00 of 10] Persistent tag cache: now with tag->node mapping

[Greg Ward]

Latest kick at the can.  It took some work and a lot of debugging, but
I got it working as Matt requested: i.e. the tag cache now includes a
copy of "hg tags" output to support "instant" tag retrieval when
nothing has changed.

The cost of this is more work on every strip: e.g. it seems to add
about 0.1 sec to the runtime of qpop for me.

Note that I have not done anything rash like run the entire test suite
on several different machines.  I'll start that now.  But this is
looking pretty promising.  (Just like the last time I sent this patch
series... sigh...)

Greg