emsdk

Fix native Closure Compiler to work. (#995)

* Fix native Closure Compiler to work. Reverts my earlier PR #803 which was a great mistake, as it caused Emscripten to silently fall back to Java version of the Closure Compiler. After this PR, Closure Compiler will work on user platforms that do not have Java installed. Also forcibly remove Java version of Closure Compiler on systems where installing the native version succeeds, in order to save on code size.

* Add note to bug

* Improve google-closure-compiler-java uninstall.

* Read Closure version from Emscripten repository

* Skip native google-closure-compiler install when it is not present in the emscripten branch in package.json

* Print error