Stylistic enhancements for durability

This is one of the oldest parts in the codebase. This commit tries to
bring the header comments and source code formatting/styling up to sync
with the rest of the code.

Change-Id: I1e7a5849b0b402c656daa467552895dc5d5f1b47
Reviewed-on: http://review.couchbase.org/41613
Tested-by: Mark Nunberg <mnunberg@haskalah.org>
Reviewed-by: Sergey Avseyev <sergey.avseyev@gmail.com>