Style change. Consolidate C<use constant> statements.
Consolidate connection closing code.

Makes connection shutdown a little more consistent.
Also fixes a bug where the wrong object ID was used to look up part of
the connection state.
Style changes.
Avoid having two different HTTP version numbers in the response status line.

Addresses a condition where response objects reported their status as
"HTTP/0.9 200 OK HTTP/1.1".
Enable POE::Kernel::ASSERT_DEFAULT during test.