* WIP: tests for #2785
* rebase onto develop
* add Bucky's test without changing ValidatorSet.Update
* make TestValidatorSetBasic fail
* add ProposerPriority preserving fix to ValidatorSet.Update to fix
TestValidatorSetBasic
* fix randValidator_ to stay in bounds of MaxTotalVotingPower
* check for expected proposer and remove some duplicate code
* actually limit the voting power of random validator ...
* fix test