Tests: a single file can now be launched with main-tests.js

give the name of the file, without the prefix 'test-' and without
the suffix '.js'.

Ex: src/slimerjs test/main-tests.js webpage-headers
Fixed a issue on webpage.evaluate()

functions as arguments for the function to evaluate, were not passed
correctly to it.
webpage.onResourceRequested should receive a networkRequest object

PhantomJs gives this second parameter. It was missing in Slimerjs.