Check for duplicate Content-Length headers in requests

If a duplicate CL header is in the request, we fail the request with a
400 (Bad Request)

Fix a test case that was sending duplicate CL by misstake and would
not fail because of that.
http_SetHeader(struct worker *w, int fd, struct http *to, const char *hdr)
{

	CHECK_OBJ_NOTNULL(to, HTTP_MAGIC);
	if (to->nhd >= to->shd) {
		VSC_C_main->losthdr++;
		WSL(w, SLT_LostHeader, fd, "%s", hdr);
		return;
	}
	http_SetH(to, to->nhd++, hdr);
}

http_SetHeader(struct worker *w, int fd, struct http *to, const char *hdr)
{

	CHECK_OBJ_NOTNULL(to, HTTP_MAGIC);
	if (to->nhd >= to->shd) {
		VSC_C_main->losthdr++;
		WSL(w, SLT_LostHeader, fd, "%s", hdr);
		return;
	}
	http_SetH(to, to->nhd++, hdr);
}
