rustc's test pass shouldn't generate calls to os::args

[brson]

For maintainability, rustc::front::test it should only be generating calls into std::test, so either there should be an os::args reexport in std::test or (my preference) test_main should contain the call to os::args and there should be a separate function for executing the console test running while providing the args.

[graydon]

non-critical for 0.6, de-milestoning

[brson]

As I see these bugs get de-milestoned I wonder how these things get milestoned in the first place. Maybe I thought it was something I would get around to, but it's clearly not important.

[catamorphism]

This already appears to be true. Closing.