HTTP: Pipelining fix #145 and improvements.

This patch fix a problem where Pipelining requests were not being
processed correctly and also do some improvements about how they are
handled internally.

Signed-off-by: Eduardo Silva <eduardo@monkey.io>

Conflicts:
	configure
	src/mk_request.c
Plugin: remove dummy trace msg

Signed-off-by: Eduardo Silva <eduardo@monkey.io>
HTTP: If-Modified-Since now allow clients from the future.

Before this patch the server did not respect a conditional
If-Modified-Since if the value was higher than the system server
date. This patch makes this pass, not a bug but make it more
friendly with Checker tools.

This patch also fix a QA script involved.

Signed-off-by: Eduardo Silva <eduardo@monkey.io>