File names with spaces are 404

[zcorpan]

In web-platform-tests/wpt#2361 (comment) I wanted to test navigating to a file named "url foo", with a space, but wptserve returns a 404 response. Similarly for getting a directory "/foo bar/" gets 404. But a wptserve directory listing includes such files.

I tried looking at handlers.py to fix this myself and search around a bit, but without luck so far. @jgraham can you take a look?