NaN is equal to NaN

[AndreasMadsen]

Fixes #83

This changes:

• t.deepEqual
• t.equal
• t.like

and there opposites

[othiym23]

This is an oddity of IEEE754, but that doesn't mean that tap should paper over it unless a developer specifically wants that behavior. IMHO this shouldn't be the default.

[isaacs]

I'd be ok with adding t.is() and t.deepIs() methods, but changing equal is not a good idea.

[isaacs]

Actually, like() is probably fine to change in this way.

[pc-dedelhart]

Can't you do an isNaN() around the result and compare the two?