hello startup-complete race

[Antoine Martin]

If a window is being resized (ie: another client keeps it mapped, or using shadow / desktop servers and randr) the new client may get a window-move-resize packet before it has had a chance to initialize the packet handlers, causing a warning to be printed.

Looks like we need an internal "startup-complete" ("handshake"? "hello"?) state flag to ignore all such events until we've been able to send the hello back. (which sets the authenticated packet handlers)
Alternatively, the client could null route them.

Similar problem for clipboard packets, which we may process before authentication is complete..

[Antoine Martin]

Fixed:

• r16386: keep track of "hello sent", don't send window packets before that
• r16387: use "hello sent" flag in more places, fix "raise_window" to honour can_send_window
• r16388: fix clipboard (removing ugly and slow special case for clipboard packets)

[migration script]

this ticket has been moved to: ​https://github.com/Xpra-org/xpra/issues/1583