client: Ignore transient_for causing loops (FS#1124)
Lots of code assumes that it can recursively follow a client's transient_for
field until it reached an end without a transient_for client. Instead of fixing
all those places to properly handle loops, this patch just makes us ignore
WM_TRANSIENT_FOR if the property causes a loop.
This means that it can be a little random which WM_TRANSIENT_FOR property is
ignored, because it will always be the one that happens to complete the cycle. I
don't think that this is bad, because there shouldn't be any loops in the first
place.
Lots-of-kudos-to: David Mohr <david@mcbf.net>
Signed-off-by: Uli Schlachter <psychon@znc.in>