Made the build/release process completable verbatim as listed in
release-process.md
Refactor: CAddressBookData for mapAddressBook

Straight refactor, so mapAddressBook stores a CAddressBookData
(which just contains a std::string) instead of a std::string.

Preparation for payment protocol work, which will add the notion
of refund addresses to the address book.
X509-validated payment requests
Refactor: Move GetAccountAddresses to CWallet
GetDataDir(): cache paths for each network separately
Rework when SelectParams is called
Payment Protocol: X509-validated payment requests

Add support for a Payment Protocol to Bitcoin-Qt.

Payment messages are protocol-buffer encoded and communicated over
http(s), so this adds a dependency on the Google protocol buffer
library, and requires Qt with OpenSSL support.