requires LWP explicitly for testing.

See https://github.com/plack/Plack/commit/478a2cca0cd9b8b70fbf3ca6d3c0550424ad42ba
Merge pull request #10 from miyagawa/require-lwp

requires LWP explicitly for testing.
support psgix.harakiri (close pull #5)
releng for 0.19
merge
renumber test