Allow for :: prefixes in _any_ call path, not just imports.

[sezna]

Right now, you can use from the root of a project like this:

use ::foo::Foo;

You cannot directly refer to something like this:

let my_enum = ::foo::MyEnum;

It isn't hard, it just needs to be done. The place to implement this would be in the places where false is passed directly in to find_module.

[emilyaherbert]

I think I have gotten myself turned around... what does the prefixed "::" indicate? As opposed to let my_enum = foo::MyEnum;.

[sezna]

It's an absolute path instead of a relative one. I.e., similar to rust's crate::foo::bar