First draft: BBDB field for saving links to messages

Only works with BBDB from mid-May, 2014, or later. Provides a custom
field type that, when present on a record, saves links to messages from
that record, allowing you faster access to recent mails from a contact.

lisp/gnorb-bbdb.el: User option `gnorb-bbdb-messages-field' specifying
		    name of field. Options
		    `gnorb-bbdb-collect-N-messages',
		    `gnrob-bbdb-define-recent',
		    `gnorb-bbdb-message-link-format-multi',
		    `gnorb-bbdb-message-link-format-one' and the face
		    `gnorb-bbdb-link' all control the specific behavior
		    of link collection. Links are collected as structs:
		    gnorb-bbdb-link.

		    Function `gnorb-bbdb-display-messages' does the
		    display, called via multi-line or one-line versions
		    of functions composed dynamically from the field
		    name. Dynamically-composed `bbdb-read-xfield-%s'
		    function prevents users from editing the field
		    directly. New function `gnorb-bbdb-open-link' either
		    opens links, when present, or starts link collection
		    for a contact. Functions
		    `gnorb-bbdb-mouse-open-link' and
		    `gnorb-bbdb-RET-open-link' do the same when point is
		    on a message link. Function
		    `gnorb-bbdb-store-message-link' added to
		    `bbdb-notice-record-hook', does the actual link
		    collection.
Whitespace/indentation cleanup

lisp/gnorb-bbdb.el
Who knew there's actually a version= function?

lisp/gnorb-gnus.el: gnorb-gnus-search-messages