usefile extension is now optional.

[Ori Bernstein <ori@xxxxxxxxxxxxxx>]

You don't need the ".use" extension when importing local usefiles any more. In
other words, instead of doing:

    use "foo.use"

you would do

    use "foo"

In the future, the .use files will be merged into the .o files, so this will
be needed to avoid breakage.

-- 
    Ori Bernstein