Rename dxr.wsgi to wsgi.py so we can put a simple one-liner in our per-deployment wsgi file.

Now the per-deployment wsgi file can say simply "from dxr.wsgi import application". We'd point mod_wsgi straight at the source tree's wsgi.py, except that it ends up at the end of a long path which contains the package version, and that will change.
Log tracebacks to Apache's error log.
Include more of the required resources in the MANIFEST so "setup.py install" installations can actually find their templates.

We have yet to figure out how to ship compiled plugins, like the clang one. Ref #110.