Currently, the Bitcoind.Dir configuration option is used as the base
directory for locating both the bitcoind configuration file and the RPC
cookie file. However, it is quite common for Bitcoin Core to be packaged
in such a way that the configuration file and the RPC cookie file reside
in different directories: "/etc/bitcoin/bitcoin.conf" and
"/var/lib/bitcoind/.cookie".
This change makes it such that --bitcoind.config and
--bitcoind.rpccookie options can be specified to override the default
auto-detection logic, and if either is unspecified, the auto-detection
logic will still do its job.
