Force streaming input onto apps by default
This change gives applications full control to deny clients
from uploading unwanted message bodies. This also paves the
way for doing things like upload progress notification within
applications in a Rack::Lint-compatible manner.
Since we don't support HTTP keepalive, so we have more freedom
here by being able to close TCP connections and deny clients the
ability to write to us (and thus wasting our bandwidth).
While I could've left this feature off by default indefinitely
for maximum backwards compatibility (for arguably broken
applications), Unicorn is not and has never been about
supporting the lowest common denominator.