Various fixes and improvements to the MIR Dataflow framework#1

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gereeter wants to merge 14 commits intonagisa:mir-dflowfrom

gereeter:mir-dflow

Commits on May 22, 2016

Commits on May 25, 2016

Remove some unnecessary `pub`s in AcsPropagate
gereeter
committed
Invalidate values in AcsLattice that are overwritten, either by a write to a projected lvalue, or through the destination of a call. Projected lvalues are now entirely not tracked.
gereeter
committed
Temporarily completely disable Backward dataflow to fix unused variant warning
gereeter
committed

Commits on May 27, 2016

Rewrite AcsLattice to be more correct
gereeter
committed

Commits on May 31, 2016

Further correctness improvements to AcsRewrite
gereeter
committed