Add a $pointer execute variable substitution and make $wip and $pid consistent (Fix...

Add a $pointer execute variable substitution and make $wip and $pid consistent (Fix bug 5758)

$wip and $pid would output values for the current target window if there was
one, but output nothing at all if there wasn't making the output difficult to
parse. Changed to make these always output a 0 if there is no target.

Added a $pointer variable that is replaced with the x and y coordiates of the
pointer, separated by a space.

Inspired by the work of Denis Kaganovich <mahatma@eu.by>.