This allows you to set a 404 handler URL on a vhost.
The necessary user code looks like...
info.error_document_404 = "/404.html";
... at vhost-creation time.
In the existing lws_return_http_status() api, if it sees
the vhost has an "error_document_404" path set and that
we are trying to report a 404, it changes the action
instead to a redirect to the error_document_404 path.
The redirect target is returned using 404 status code.
If the redirect target doesn't exist, then it falls back
to just reporting the simple canned 404.
This enables selected things from -Wextra, can't use -Wextra because it is
fussy enough to complain about unused params on functions... they are
there for a reason.
-Wsign-compare
-Wignored-qualifiers
not -Wimplicit-fallthrough=3 ... only on gcc 7
-Wtype-limits
-Wuninitialized
not -Wclobbered ... only on gcc 7ish
fix the warnings everywhere they were found.
