build: added deletion of stale .so and .o files

build: added deletion of stale .so and .o files

when we change our build rules to move a C file, we need to remove the
old ('stale') .so and .o files from the build directory, or they may
be used as part of the new build, which means that old code will be
linked in.

This expands the list of stale files that we remove on rule changes to
include .so and .o files

Pair-Programmed-With: Amitay Isaacs <amitay@gmail.com>

Autobuild-User: Andrew Tridgell <tridge@samba.org>
Autobuild-Date: Wed Oct 19 09:02:23 CEST 2011 on sn-devel-104