Ajax: Add support comment and fix code style issue

Closes gh-1600
Ref e5190982c40d7ac8ab9bdb2e7e4334f0e123ef66
Ref #8138

src/ajax.js

@@ -44,6 +44,7 @@ var
 	// Avoid comment-prolog char sequence (#10098); must appease lint and evade compression
 	allTypes = "*/".concat("*");
 
+// Support: IE<8
 // #8138, IE may throw an exception when accessing
 // a field from window.location if document.domain has been set
 try {