Do some sanitization on traits.

    - Remove tctest: all tests now take a boolean.
    - Rename traits to more sensible names:

        tcnum => numeric
        tcint => integral
        tcfloat => floating
        tcidx => indexable
        tcslice => sliceable

    - Remove duplicate trait setting.
        We were setting traits twice in some places, adding
        ones that didn't belong, which was making pointers look
        indexable.