Primecoin HP: Added support for donations via -donationpercentage parameter.
Primecoin HP: Optimize GetBlockWork() by using shifting instead of repeated multiplication.
Speeds up startup slightly.
Optimize repeated bignum multiplications etc by reusing the same BN_CTX. Use lazy initialization inside the CAutoBN_CTX.
Primecoin HP: Added the declaration of nWorkTransitionRatioLog which was missing from commit b6a92cd8b9.
Merge branch 'master' of https://github.com/mikaelh2/primecoin into experimental

Conflicts:
	src/bignum.h
NOT finished yet, DO-NOT-TOUCH :)