Define externally accessible contants with 'var' instead of 'const'

Just as we did with classes, define other constants that are (or
may be) used from other modules with 'var' to cut down on warnings.

https://bugzilla.gnome.org/show_bug.cgi?id=785084

js/misc/util.js

@@ -14,7 +14,7 @@ const Main = imports.ui.main;
 const Tweener = imports.ui.tweener;
 const Params = imports.misc.params;
 
-const SCROLL_TIME = 0.1;
+var SCROLL_TIME = 0.1;
 
 // http://daringfireball.net/2010/07/improved_regex_for_matching_urls
 const _balancedParens = '\\((?:[^\\s()<>]+|(?:\\(?:[^\\s()<>]+\\)))*\\)';