Use correct and non-hardcoded buffer sizes

The magic values 44 and 10 were harder for a reader to guess and
larger than necessary. The new and correct values also end up saving
57 bytes per doc info record.

Change-Id: Ieeff565d96acc929b43245686126228d3b401161
Reviewed-on: http://review.couchbase.org/27454
Reviewed-by: Aaron Miller <apage43@ninjawhale.com>
Tested-by: Aaron Miller <apage43@ninjawhale.com>
Reviewed-by: Volker Mische <volker.mische@gmail.com>
Tested-by: Filipe David Borba Manana <fdmanana@gmail.com>