Fix encoding issues with the search prompt

In Firefox and Chrome, the string returned from prompt is already
encoded. I couldn't find any formal specification on this behaviour at
first glance. This should definitely be tested on other browsers.

flamegraph.pl

@@ -823,7 +823,7 @@ sub flow {
 	function parse_params(params) {
 		var uri = "?";
 		for (var key in params) {
-			uri += key + '=' + encodeURIComponent(params[key]) + '&';
+			uri += key + '=' + params[key] + '&';
 		}
 		if (uri.slice(-1) == "&")
 			uri = uri.substring(0, uri.length - 1);