do not load backup files from /etc/X11/xinit/xinitrc.d

source only known *.sh files

see also similar thread in xinitrc-ng
http://lists.pld-linux.org/mailman/pipermail/pld-devel-en/2012-January/022432.html

and http://svn.pld-linux.org/trac/svn/changeset/12470/xinitrc-ng/trunk/xinitdefs