fixed typo in comment in netbase.h and bignum.h

fixed typo in comment in netbase.h and bignum.h

* Improved exception handling
 - Removed attempts to catch exceptions in intermediate helper function calls
 - Made helper functions for JSON parsing private

* Governance voting fixes
 - Converted voting defines to enums for better type safety
 - Enabled gobject voteraw rpc command
 - Removed unused parameter from gobject getvotes rpc command

* Fixed help message for gobject get

* Improved encapsulation of CGovernanceVote objects
 - CGovernanceVote data members are now private
 - Necessary to ensure that enum values are used for signals and outcomes since data members remain int's for compatibility with serialiation code

* Removed unused cs_budget mutex (has been replaced with governance.cs)

* Fix code review issues
 - Restored early return in ConvertVoteSignal
 - Removed special case for "none" string to make clear that NONE is
   for invalid strings
 - Removed commented defines (informational comments preserved)

* Fixed code review issues
 - Fixed error messages for vote-conf, vote-alias and voteraw
 - Removed voteraw from gobject command list and help messages because
   it is actually a top-level command
 - Fixed parameter indices for voteraw

Move checking of blockdownload timeout to the request manager

e06f7b6 [Tests] Minor optimizations in zerocoin_valid_public_spend test (random-zebra)
cdc18ea [RPC] fix parameters check for spendzerocoin (missing ispublicspend) (random-zebra)
72bc39a [Tests] Add zerocoin_valid_public_spend to testRunner (random-zebra)
26045d3 [Consensus] Set zc PublicSpend version v3/v4 via SPORK (random-zebra)

Pull request description:

  This follows bitcoin#936
  It sets the required version for zerocoin PublicSpends via SPORK instead of having it height-based.

  When `SPORK_18_ZEROCOIN_PUBLICSPEND_V4` is not active (default), the required version is v3 (where old version 1 serials cannot be spent. ref: bitcoin#891 ).

  It also fixes the relative functional test `zerocoin_valid_public_spend.py` and adds it to the test_runner.

ACKs for top commit:
  furszy:
    utACK e06f7b6
  Warrows:
    utACK e06f7b6

Tree-SHA512: 07f18e77a91503f5d48dafad32364cc6292ffd1f9a3f9286a78de72dafc98b07342e6abd96eaabe55d20193f10be383c8d5bbac1b33c45712ade8c522e457b3f