As QWindowsPipeWriter now maintains a chunk queue, there is no need to
use the internal QIODevice buffer and wait for the previous operation
to complete.
This also allows us to get rid of the stdinWriteTrigger timer; however,
as a trade-off, QWindowsPipeWriter now needs to accept data even before
a handle is assigned.
Change-Id: I17fe0e36a6165fe05100bfab3fe01fc0d880d617
Reviewed-by: Oswald Buddenhagen <oswald.buddenhagen@gmx.de>
79490d2a4c