Fix import errors for case-insensitive filesystems

If you have a case-insensitive filesystem (or even a VM running on
top of a case-insensitive filesystem) you will get import errors.

For example, TileStache's Mapnik.py has an "import mapnik" call.
Since the filesystem is not distinguishing mapnik.py from Mapnik.py
it re-imports itself and then fails. We can fix this by enabling
absolute imports.
Remove 'host' from test conn strings