Fix divide by zero bug.
Bignum doesn't have a bool cast?
Fix "expectedtime" estimate returned by RPC call "getstakinginfo".

It was wrong before, using nTargetSpacing rather than nTargetStakeSpacing, and ignoring current difficulty.
Merge branch 'better-staking-estimate' of git://github.com/dooglus/clams into dooglus-better-staking-estimate
Merge branch 'dooglus-better-staking-estimate' into develope