Implement "new-style" name_firstupdate operations.

After a planned hardfork, allow name_firstupdate operations to take
place without a preceding name_new.  In this case, no hash/rand value is
present, and no checks are done for this.  This will allow simpler name
registrations in the future, at the loss of protection against "name
stealing" -- which seems no big deal in Huntercoin anyway.
Add RPC call for new-style registration.

The new RPC command 'name_register' performs new-style name
registration.  Also fix a problem with mining these.
Use AllowNewStyleRegistration in RPC code.
Merge pull request #86 from domob1812/name-new

Simpler "one step" name registration