Library regression test should not use prettified baseline.

As suggested by Bei Zhang, the JSON version of the syntax tree and
the tokens consume less space when it is not indented.

https://code.google.com/p/esprima/issues/detail?id=509
Utilize gc() for V8 and SpiderMonkey

https://code.google.com/p/esprima/issues/detail?id=529
Fix coding styles in test/benchmarks.js.

https://code.google.com/p/esprima/issues/detail?id=529
Remove duplicate markEnd

https://code.google.com/p/esprima/issues/detail?id=528