Add support for cloning over http

This patch implements basic support for cloning over http, based on the
work on git-http-backend by Shawn O. Pearce.

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

html.h

@@ -5,6 +5,7 @@ extern int htmlfd;
 
 extern void html(const char *txt);
 extern void htmlf(const char *format,...);
+extern void html_status(int code, int more_headers);
 extern void html_txt(char *txt);
 extern void html_ntxt(int len, char *txt);
 extern void html_attr(char *txt);