Force space after literal regexp when used in "instanceof" or "in"

Close #118

lib/output.js

@@ -1081,6 +1081,9 @@ function OutputStream(options) {
         if (output.option("ascii_only"))
             str = output.to_ascii(str);
         output.print(str);
+        var p = output.parent();
+        if (p instanceof AST_Binary && /^in/.test(p.operator) && p.left === self)
+            output.print(" ");
     });
 
     function force_statement(stat, output) {