Addressed comments
Addressed comments

Added comments to explain why we're clearing out the whole bit vector
Cleaned up the backward pass specific code
Changed -= to = &~ for removing BailOutOnNegativeZero

mrkmarron/ChakraCore,Microsoft/ChakraCore,Microsoft/ChakraCore,mrkmarron/ChakraCore,mrkmarron/ChakraCore,mrkmarron/ChakraCore,Microsoft/ChakraCore,mrkmarron/ChakraCore,mrkmarron/ChakraCore,Microsoft/ChakraCore,mrkmarron/ChakraCore,Microsoft/ChakraCore,Microsoft/ChakraCore