Squashed commit of the following:

commit 5ff05dad8d46a3ab23a952602bb8c66fbc5ae083
Author: Mark Johnston <markjdb@gmail.com>
Date:   Thu Mar 28 11:47:46 2013 -0400

    Add if_bridge(4).

commit 14cd853acc04125cfaf540d09c87a29ddf6a3390
Author: Mark Johnston <markjdb@gmail.com>
Date:   Sun Mar 24 17:50:52 2013 -0400

    Add a custom kernel configuration file for my laptop.
Move some generic kernel core buffering code out of arch directories.

The kernel dumping code does some write buffering and the code for this
is completely generic. Move it to a generic file instead of duplicating
it on all architectures.