fix stupid bug in reducer

remove a debug printout

assert that souper-check likes the initial input to the reducer
Invoking PrintReplacementLHS for dumping all replacements

Because RHS is NULL after we switched to infer mode,
we need to use PrintReplacementLHS rather than PrintReplacement.
Otherwise, souper pass would crash by passing -souper-debug-level=2.
Merge pull request #100 from chenyang78/debug_level

Invoking PrintReplacementLHS for dumping all replacements
Fixed divide-by-zero crash for issue 84

We can't pass a constant zero as a divisor when building KLEE expressions,
because KLEE invokes llvm::APInt's div functions, which crash on zero value
divisors.

To fix this, when we build a div/rem expression, we fist check if the second
oprand is klee constant 0. If it is, then it definitely causes UB, and we
simply skip building the corresponding KLEE expression and just return a
constant zero.
Merge pull request #99 from regehr/reducer-fix

reducer fixes
Merge pull request #102 from chenyang78/issue_84

Fix to Issue #84
Merge remote-tracking branch 'origin/master' into remove-istriviallyinvalid
fix tests as in Peter's feedback