See r26433.
When using an xterm with --pixel-depth=30 and a client with a 24 bit display (that's over 99% of them), we convert r210 to BGRA and only restride afterwards.
So we end up copying huge amounts of data, only to discard it on the next step.
Done in r26891.
this ticket has been moved to: https://github.com/Xpra-org/xpra/issues/2773