Add switch benchmark.
Stop negating checks.
Add a 'switchify' optimization pass. Refs #1278.

Converting if-elses to switch-case could *potentially* change a O(N)
series of tests into an O(1) lookup.
Reduce clause count threshold for switch creation.

Makes tests easier to write. May change it back later if it proves
suboptimal, but right now we don't know either way.
Fix switchification of top-level ifs.
Switchify if-else clauses with negations too.
Fix optimization pass order.
No need to assume that if/else bodies are nonempty.
Make switchification the default.
Make print_stats more generic.
Always print out totals
We can now benchmark JS-to-JS in one step.
Add heuristics for switchifying.

Also hack the settings system so we can parameterize these heuristics
from the command line.
Further generalize the benchmark framework.

We can now specify tests with various arguments using an external file.
Allow serialization of benchmark results.

This allows us to do more post-analysis. E.g. make graphs.
Fix switch density calculation.
oops
Add test for switch density.
Mistake from rebasing
Add the meteor-contest benchmark for Lua.