Make sure pty device has right size before terminal process queries it.

Whenever TeminalDisplay is resized, konsole tells the underlying
pty device its new size by calling Pty::setWindowSize(). However,
current code can't guarantee when the terminal process starts and
queries the pty device about its size, the pty device already has the
right info. This has caused some long known bugs, such as #176902.

This patch tries to guarantee that important assumption. It currently
uses a hard-coded small delay, which works pretty well in practice
although not that elegant.

Patch by Jekyll Wu <adaptee@gmail.com>

I think this is better than leaving the situation as it is.  This may
be backported if no issues are found.
BUG: 173999
BUG: 176902
BUG: 203185
BUG: 229058
REVIEW: 102061
FIXED-IN: 4.8