At the same time, fix an old error in prestel_handle_escaped() that
didn't pass the ctrl to prestel_apply_ctrl_after() properly, and
always flush the print buffer before calling prestel_handle_escaped()

We still shouldn't actually get C1 characters on a Prestel connection,
but if we do, at least we're doing the right thing now.

As for G1 characters, the default repetoire for these terminals per
ITU-T REC. T0101 is the mosaic character set with smoothed moasics,
something there's no evidence of a Prestel terminal ever supporting.
In order to implement those properly, I would need special handling
of "separated" in the renderer, and would need to fiddle with the
font to include the contiguous smoothed mosaics (and exclide the
separated ones).  Since this would end up allowing wildly un-Pretel
behaviour (ie: mosaics without a mosaic escape) I'm inclined to
just treat them all as spaces and move on util/unless I do full
support for all the Videotex standards.  Nobody has asked me to
open this can of worms, so I'm just going to leave it on the shelf.