CCBC-319: Expose vbucket symbols

Note that we don't yet ship the headers for vbucket, but with this
modification it should be possible to define the API symbols themselves
(inline) and use them from the symbol table

Change-Id: I2a394ad78b2152da2f7373eb1c907e837233e784
Reviewed-on: http://review.couchbase.org/33173
Reviewed-by: Brett Lawson <brett19@gmail.com>
Tested-by: Mark Nunberg <mnunberg@haskalah.org>