fix handling of x11 ICCCM WithdrawnState

fix handling of x11 ICCCM WithdrawnState

according to ICCCM 4.1.4:
Only the client can effect a transition into or out of the Withdrawn state

withdrawn windows cannot be shown under any circumstances. the best that can
be done is to try mapping the window and hope it decides to appear.

to prevent any inadvertent showing of the window before it leaves the
withdrawn state, we play games with the E_Client->ignored flag in order
to skip client evals until we get notified that maybe we want to stop
skipping those evals

ref T2745