Implement name_update in createrawtransaction.

Add support for name_update operations in the createrawtransaction RPC
call with a new, optional third argument.
Merge branch 'rawtx-nameupdate' of github.com:domob1812/namecoin into rawtx-nameupdate
Merge branch 'namecoinq' into rawtx-nameupdate
Merge branch 'rawtx-nameupdate' of github.com:domob1812/namecoin into rawtx-nameupdate
Merge branch 'namecoinq' into rawtx-nameupdate