use writeback to external io handler in transport_write if external io
is in use

logic fix

implemented write handler for external io

added support for external io mode into transport_read_pdu
instead of duplicating it.

added missed EOL in new file

logic fix

dropped unneeded 'else'

WIP: making whole io switchable

moved streampool related code to separate function

implemented switchable Read

implemented switchable write

changes requested by akallabeth

DataHandler inplementation should not be switched, it is intended to be
used from external user
use SSIZE_T type for signed size type

improoved 'freerdp_set_transport_callbacks' logic a bit

overwrite already allocated rdpIoUpdate instead of changing pointer to
new one

dropped noisy log messages

more agressive "polling"

requested

This reverts commit f4c8041.

transport_register_default_io_callbacks require update->context to be
set

implemented global io timeout for transport io, by default set to 60
seconds

working on switchable connect/disconnect functions

returned SetEvent/Resetevent for ransport->rereadEvent and
transport->haveMoreBytesToRead  state setting, as server side code
depends on it (ned to be eliminated in further refactoring)
in server/Sample used 1000 timeout for WaitForMultipleObjects as
workaround, looks like WaitForMultipleObjects does not work properly.

corrected padding in io struct