CMake-ify distribution information

This moves the top-level packaging information from the source tree and
places it into packaging/distinfo. The VERSION script is now replaced by
a proper CMake script (generated when appropriate).

The global 'CHANGESET' is no longer used, rather being replaced by
'LCB_VERSION_CHANGESET'. This removes some weird regexp parsing within
the CMake scripts.

Change-Id: I0f0cf11fd5df0e9d69909e52f64f58e9982148bc
Reviewed-on: http://review.couchbase.org/43715
Tested-by: Mark Nunberg <mnunberg@haskalah.org>
Reviewed-by: Sergey Avseyev <sergey.avseyev@gmail.com>