Document kill_script process runner option.
Depend on newer istanbul version which supports --complete-copy.
Use new --complete-copy flag with istanbul. This way it works in the same way
jscoverage did in the past.
Merge pull request #62 from cloudkick/upgrade_istanbul

Upgrade istanbul
Add rewire to TestFile.runTests() so when coverage is running, the test
module has the covered resources in lib/ injected into its scope.

Remove the lib-cov in NODE_PATH requirement as it isn't needed with
rewire