Detect Tautologies

Example contract:

contract MyContract {

  function foo(uint256 a) returns(uint256) {
    if(a >= 0){ //this will never be false
      return 0;
    }
    return 1;
  }
}```

Mythril should detect a comparison which is always true, at least one as simple as this. 

[muellerberndt]

We should call it Muffle. Mythril + Truffle.

Or not.

[muellerberndt]

My main concern is that if we simplify the CFG by removing paths that are unreachable for particular concrete values, there might be a chance for false negatives to occur. Specifically if an error state is reachable via multiple transactions (e.g., a variable needs to be initialized first). This isn’t that relevant right now as long as inputs are largely symbolic, but might become an issue when we start using concrete initial states.