Fix incorrect sort behavior due to UglifyJS bug.

UglifyJS version 2.2.5 incorrectly performs the transformation:

  (x = f(…)) <= x → x >= (x = f(…))

This caused incorrect sorting behaviour when using crossfilter.min.js.

All tests now pass on crossfilter.min.js.
Update UglifyJS and revert workaround.

All tests pass on the minified version.  This version of UglifyJS fixes
a serious bug involving reordering of side-effects.