2014-03-31  Antonio Gomes  <a1.gomes@sisa.samsung.com>

        Events can be omited but can not be set as 'null'
        Issue #504

        Found by Anthony Liot.

        Fixed BoxFilter translated demo:
        http://wolfviking0.github.io/webcl-translator/build_nvidia/index.html?sample=2&gl=on&title=BoxFilter&gpu

        * Modules/webcl/WebCLCommandQueue.idl:
        * Modules/webcl/WebCLProgram.idl: