use state monad in satchmo backend
add clause-length histogram
Merge branch 'master' into experimental

Conflicts:
	Satchmo/Core/SAT/Minisat.hs
	satchmo-core.cabal
add minisat-0.2 dependency
count literals in minisat backend
Merge branch 'master' into experimental

Conflicts:
	Satchmo/Core/SAT/Minisat.hs
	satchmo-core.cabal