Verification levels must be between 0 and 4 inclusive, and block heights should
always be positive. While code in the scan process handles the latter case with
a default value, it's better to verify and reject invalid input where it first
enters the system.
Fix pruneheight help text.
Move fPruneMode block to match output ordering with help text.
Add functional tests for new fields in getblockchaininfo.
Rebase-from: bitcoin#b7dfc6c4
* Make most of the RPC tests pass
* Add AUXPoW rpc tests
- Tests the auxpow rpc interface `getauxblock`
- Tests consensus constraints for auxpow:
- Minimum block height
- Valid scrypt proof of work
- Foreign chain ID
