Add another test which looks at the effects of the program's original
synchronisation.
Another test looking at the effects of any existing sync which the
program might have.
If the CDG can show that certain edges are unused then that sometimes
leads to misbehaviour in realias.  Easy fix: just invalidate the CDG
and go around again.
Redo removeTerminalStores:

-- Cost goes from O(n.2^n) worst-case to O(n^2) worst case.
-- It now includes a timeout check, so even if it does take bloody ages
   it won't completely screw a run.
BDD ordering treats ControlFlow and EntryPoint expressions as
equivalent, so optimisations which depend on ordering should as well.
Add some sanity checking to make sure that when we try to remove the
HB edges we actually succeed.
Get rid of a silly hack which is no longer necessary.
Make summary_to_interp do something sensible if enforce_crash comes
up with an empty CED.
Merge github.com:sos22/SLI
gcc sometimes generates nop instructions with a CS prefix, for some
reason.  Make sure we can correctly handle them.
It is actually possible for a root of the CFG to have predecessors,
because of the slightly odd definition of root.  We consider an
instruction to be a root if we can transition to it from
non-interpreter mode, but that's not exclusive with also being able to
transition to it from interpreter mode.  Make sure this is handled
correctly.
Remove any entry points which can't reach any relevant memory
accesses.  This doesn't really help all that much, but it does reduce
the number of times the CEP interpreter reports success without
actually causing a crash, which makes the results a bit easier to
interpret.
Move the CEP debug fluff to file descriptor 2, so that it doesn't
conflict with pbzip2 output.
Try a bit harder to remove redundant roots from the CEP.  Again, this
doesn't change what actually happens, but it makes the results easier
to interpret.
Unbreak new format callgraphs again.
Merge commit 'f2b6afe'
Shiny new available expression analysis.  Avoids some of the stupid
performance horrors of the old one, and is also a lot simpler and more
obviously correct.