Move the timings-specific pieces of the buildbot infrastructure into

Move the timings-specific pieces of the buildbot infrastructure into
the trunk/timings directory.  We'll map them into the buildbot directory
using svn:externals.  This will let us keep all the pieces of a timing
configuration, including its buildbot pieces, in one place, and will
let us simplify the Master initialization (since it will be able to look
on-disk for the configurations for which it should set up buildbot steps,
instead of querying the SVN server).

git-svn-id: http://scons.tigris.org/svn/scons/trunk@4562 fdb21ef1-2011-0410-befe-b5e4ea1792b1