Misc. Warning and cosmetic error cleanups.

This fixes a cosmetic precedence bug in the tests along with some
 type warnings.

It also adds a dummy cast to the CHECK macro to avoid hundreds
 of statement with no effect warnings on compilers that warn about
 such things.
Remove some dead variables in the tests.
Merge pull request #77

1d52a8b Implementations for scalar without data-dependent branches. (Pieter Wuille)
Merge pull request #95

79ad6d4 Remove some dead variables in the tests. (Gregory Maxwell)
9974d86 Misc. Warning and cosmetic error cleanups. (Gregory Maxwell)
Use Montgomery multiplication for scalar inverses.
Some simplications in the muladd sequences