ui-shared: add support for NO_HTTP=1/--nohttp

cgit_print_http_headers() used to do nothing if 'embedded' was
specified in cgitrc, but that was wrong - we never want to skip the
headers when invoked as a CGI app. Sadly, there's no easy way to
detect if we're invoked as a CGI app or if we're invoked by another
CGI app, so for the latter case cgit needs to be invoked with either
--nohttp on the command line or NO_HTTP=1 in the environment.

Signed-off-by: Lars Hjemli <hjemli@gmail.com>

ui-shared.c

@@ -455,7 +455,7 @@ void cgit_print_age(time_t t, time_t max_relative, char *format)
 
 void cgit_print_http_headers(struct cgit_context *ctx)
 {
-	if (ctx->cfg.embedded)
+	if (ctx->env.no_http && !strcmp(ctx->env.no_http, "1"))
 		return;
 
 	if (ctx->page.status)