vc-state-heuristic is gone

[Eric S. Raymond]

First, easiest gain from attacking the VC backend API with fire and
sword:  vc-state-heuristic is gone. vc-stay-local is probably next.

These were attempts at performance optimizatiion that made sense when
disk and network operations were much slower than they are now.  I
remember quite clearly that when I first wrote VC mode in 1992 I spent
the majority of my effort on thinking up ways to avoid hitting the
disk.

But the tradeoffs have changed.  The operations I was trying to avoid
are much less expensive today, but the cost of the bugs and edge
conditions produced by incautiously doing repository operations behind
Emacs's back (and this rendering the caching and heuristics involved
ivalid) has not dropped.  If anything, it has risen.

Thus, a brutal and effective simplification: *all caching goes away*.

Affected back ends: SCCS, RCS, CVS, SVN, Bazaar.  I've already tested
with RCS and any change in preformance is now so small that a human is
not capable of registering it.
-- 
                <a href="http://www.catb.org/~esr/";>Eric S. Raymond</a>

A nation or civilization that continues to produce soft-minded men
purchases its own spiritual death on an installment plan.
        --Martin Luther King, Jr.