Less order indirection

These are some small performance improvements for `Map` order, `IndexedSeq` order, and `Order` methods.

The former two have the funny property that they sacrifice some predictability for performance in sorting heterogenous sequences.  For example, in the sorted `Iterable[IndexedSeq[A]]`, producing the sorted iterable will be faster if the seqs have different sizes, and supposing that, comparison of consecutive seqs closer to the end of the iterable takes longer than for those closer to the beginning.

Of course, this is simply a different set of arbitrary trade-offs than the ones made previously.