1. Added a --traceEmitNode option to add print traces of all emit node
functionality. This is helpful considering the lack of single stepping

2. Still resolving the issue of removing symbols created and reflected
during the autotuning process. The simplest way would be to checkpoint
internal compiler state before search and restore it to that state after the
search. State exists in two places: Expressions (globalDefsCache,
globalDefs, localDefs), and Effects (context). The "purgeAndResetSym"
function in Expressions removes symbols from a certain number upto the
current symbol from Expressions, while "purgeSymFromAll" removes it from
both Expressions and Effects.

Haven't tested this yet.