Because of the way that a FormBodyServletRequestWrapper was
implemented (extending the Zuul servlet 2.5 wrapper) it could
barf at runtime if anyone called its servlet 3.0 methods. The fix
for that was to extract our Servlet30RequestWrapper and extend that
instead.

Also tweaked the DebugFilter a bit so it doesn't try and display
the whole payload. Probably speeds up file uploads a bit but the
fact that we have to store the whole request body in memory is
going to kill us eventually.

See gh-254