Speedup startup

[mroderick]

TL;DR Use cache-require-paths to make Buster.JS start faster, ~700ms faster on my machine.

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Cache node's require lookups for considerable speedup.

To verify

Measure time to run tests with time in a buster dependent project

time buster-test

Checkout this branch and use npm link to make a buster dependent project use this version of Buster.

Repeat the time measurement a couple of times (first succesful one writes the .cache-require-paths.jsonfile).

Calculate any improvement over current Buster.

Results

On my machine with a small project running tests only in node

281 tests, 336 assertions, 1 runtime

	Before	After
real	0m1.969s	0m1.254s
user	0m1.356s	0m1.144s
sys	0m0.189s	0m0.090s

Speedup: 1969 - 1254 = 715ms

(caveats: on my machine, in my project, using node@0.10, today)

I think the difference is significant enough to add this dependency.

[dominykas]

So far I have two problems with this

• the cache file is not cleared automagically - if I hadn't suspected this is the culprit, I'd probably wouldn't have figured it out, but after yet-another-npm-install the dep tree reshuffled and things started failing
• people who check their node_modules into source control might not be happy with an extra file appearing and changing (which includes hardcoded paths, which will fail on other people's machines as per above point)