Change scanner to properly search for included file from the

Change scanner to properly search for included file from the
directory of the main file instead of the file it is included from.
Also update the emitter to add the .aux file associated with
\include{filename} commands. This makes sure the required directories
if any are created for variantdir cases.
Half of the patch from Stefan Hepp.

git-svn-id: http://scons.tigris.org/svn/scons/trunk@4591 fdb21ef1-2011-0410-befe-b5e4ea1792b1