CKBuilder: Closure Compiler thinks native is a reserved keyword

[Wiktor Walc]

It it impossible to build CKEditor after this change: ​a2136ce (native sis a reserved keyword). I remember that it happened at least in the past. We renamed the "native" variable to "nativ".

After a quick research it turned out we may get rid of this issue forever by using this piece of code:

options.setLanguageIn( CompilerOptions.LanguageMode.ECMASCRIPT5 );

native was a future reserved word in ECMAScript v3. Closure Compiler follows ES4, which also lists native as a reserved keyword.

However, I believe it will be quite unsafe to switch CC to ES5 mode at this moment, because this time we may not notice code that will be incompatible with IE7.