Updated CJuiButton sample, to reflect correct parameters [ci skip]

Updated CJuiButton sample, to reflect correct parameters and normal usage [ci skip]
Merge pull request #2647 from luislobo/patch-4

Updated CJuiButton sample, to reflect correct parameters [ci skip]
better doc for UnsafeValidator::validateAttribute
added warning about appending autoloader

include path will be disable so use with care!
fixes #2638