fix & improve AST_TemplateString (#2410)

- resolve `semicolons:false` ambiguity with tagged literals
- allow `side_effects` to work on template literals
- traverse `AST_TemplateString` properly

fixes #2401

lib/output.js

@@ -262,7 +262,7 @@ function OutputStream(options) {
         }
     } : noop;
 
-    var requireSemicolonChars = makePredicate("( [ + * / - , .");
+    var requireSemicolonChars = makePredicate("( [ + * / - , . `");
 
     function print(str) {
         str = String(str);