Support validation of requests

[thboileau]

Initial ticket : http://restlet.tigris.org/issues/show_bug.cgi?id=781

[jlouvel]

From original ticket:

It would be useful as a service to enforce some limitation. The control could be
based on the declared entity length if known or on the actual length received
(how?).

This filter/service should set the status to 413 in this cases:
http://www.w3.org/Protocols/rfc2616/rfc2616-sec10.html#sec10.4.14

We should also verify and limit the length of URIs, setting the 414 status if
necessary:
http://www.w3.org/Protocols/rfc2616/rfc2616-sec10.html#sec10.4.15