unbreak XDG_CONFIG_DIRS and by extension autostart
"If $XDG_CONFIG_DIRS is either not set or empty, a value equal to /etc/xdg should be used." If XDG_CONFIG_DIRS was not set prior to startplasma, which it ordinarily would not be, then the previous code would set the value to "$newdir:" which was silly and also wrong as per the spec quoted above. Instead default to /etc/xdg/. Also camelCase the variables to follow our coding style.