Several improvements to InfoFlowAnalysis.h

1) Perform meet of function parameter dataflow values only when doing a must analysis
2) Use SetVector for the worklist
3) Slight rewrite of the propagateToCallees function so that we first iterate through the call arguments and then the callees. This simplifies the logic and leads to faster execution.
4) Remove warnings for when not being able to find the var args list variable and also for when encountering an unknown instruction in propagateToAggregate
5) In propagateToAggregate, propagate dataflow state to all intermediate values encountered