Trim trailiing whitespace
Only init mimetypes if it isn't already; #148

See comment inline for more info. This is a workaround for a big test
slowdown that we're seeing between master and the spt branch. Need to
look into that.
Fix up the rest of the tests; #148

The tests are passing, though they're super slow. The only way they pass
at all for me is with that mimetypes.init conditional in the last
commit.