Advise the kernel that we will scan DB files sequentially.

Advise the kernel that we will scan DB files sequentially.

src/recdb.c (parse_database): Advise the kernel that we will scan the
    recdb file sequentially, just in case it cannot notice the access
    pattern on its own.
git-archimport-id: srvx@srvx.net--2006/srvx--devo--1.3--patch-6