Set version number for the given package name.

@param {String} packageName The package name, for example: 'core', 'touch', 'extjs'
@param {String/Ext.Version} version The version, for example: '1.2.3alpha', '2.4.0-dev'
@return {Ext}
function(packageName, version) {
            Ext.versions[packageName] = new Version(version);
            Ext.lastRegisteredVersion = Ext.versions[packageName];

            return this;
        }