Various improvements

I'm sending this after being mentioned in https://github.com/jruby/warbler/pull/133#issuecomment-12888698.

Sorry for non-informative pull request title, but this PR is best described by the commit list.

The most important one is definitely https://github.com/whitequark/warbler/commit/04f5f404cb52e961fdac673430e52eeccd1bace1.