feat(collapse): Remove transition-canceling for TWBS3.0 compat

Nice looking transition animations with the following browsers, on
OSX 10.8.4:

Chrome29.0.1547.65
FireFox19.02
FireFox23.01
FireFox26.0a1 (2013-09-04)

No 'bogus state' issues with unfinished animations (that I've seen,
as of yet).

Unfortunately, there are some failing tests (on each browser), because
some functionality had to be dropped to work well. These tests have not
been rectified yet.

There are some helpers for providing more robust information about the
dimensions of the collapsing object, which I've included in a 'helpers'
object. These should probably be either discarded, or else moved to a
more central location where they can be shared by other components.
Just a thought. (The implementations of these functions has been adapted
from Prototype, and may not be quite as robust as jQuery).