Added 'headers' field to opts for request/relax. This gives you the a…

…bility to pass in request headers.

nano.js

@@ -124,6 +124,12 @@ module.exports = exports = nano = function database_module(cfg) {
       req.uri = u.resolve(req.uri, opts.db);
     }
 
+	if (opts.headers) {
+		for (var k in opts.headers) {
+			req.headers[k] = opts.headers[k];
+		}
+	}
+
     if(opts.path) {
       req.uri += "/" + opts.path;
     }