Avoid processing files even if they are specified in a "//= require" statement

[Gianluca Sartori]

Some .js files are not compatible with the processing from the Closure Compiler and they throw exceptions.

We can exclude them, but if they are part of a //= require the exclusion does not work.

We would like to use already minified .js files in a //= require without them to be processed from the Closure Compiler.