Support sites without clean urls.

Attached patch enables multidomain to work without clean urls.

We need to put a ?q= in the path if clean urls are not available. We also need to modify the patch to common.inc so as not to put that in if it's a url we've already rewritten.

Of course, we need to assume that all the domains have the same (either all clean urls or all not clean urls). This seems a safe assumption.