Revise git ignore files

Revise git ignore files

Revise our git ignores to match the current state of the tree, and include
entires in the top level for all of the 'dest' directories for all of the
architectures we claim to support.

Reviewed-on: http://gerrit.openafs.org/2
Reviewed-by: Derrick Brashear <shadow@gmail.com>
Verified-by: Simon Wilkinson <sxw@inf.ed.ac.uk>