name_pending and getchains RPC commands

This patch ports over two RPC commands from Huntercoin:

name_pending:  Shows pending name_update and name_firstupdate transactions in the memory pool.  This can be useful both for a future RPC-based UI (to show, for instance, your own pending transactions) and also for general-purpose debugging / block explorers or whatever.

getchains:  Show information about all known blocks and their relationship in the "tree" of known blocks.  This can be used to find and analyse chain forks and orphan blocks.