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_Init(void)
{

#define HTTPH(a, b, c, d, e, f, g) b[0] = (char)strlen(b + 1);
#include "http_headers.h"
#undef HTTPH
}

HTTP_Init(void)
{

#define HTTPH(a, b, c, d, e, f, g) b[0] = (char)strlen(b + 1);
#include "http_headers.h"
#undef HTTPH
}
