Implementations for scalar without data-dependent branches.
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 Co-Z arithmetic for precomputations

- Selected Co-Z formulas from "Scalar Multiplication on Weierstraß Elliptic Curves from Co-Z Arithmetic" (Goundar, Joye, et. al.) added as group methods with new type sep256k1_coz_t.
- Co-Z methods used for A and G point precomputations.
- WINDOW_A size increased to 6 since the precomputation is much faster per-point.
- DBLU cost: 3M+4S, ZADDU cost: 5M+2S.
- Take advantage of z-ratios from Co-Z to speed up table inversion.

Conflicts:
	src/ecmult_impl.h