Console: provide VT100-like end-of-line print behavior.

On the majority of VT100-like terminals, when you print a
character in the last column, the cursor sits in a kind of
"limbo", as if the cursor position were one column past the
edge of the screen. Thus when a line feed is output next,
the cursor is then at the start of the next line.

The Win32 console write doesn't do this; the cursor position
wraps to the start of the next line. If a newline is put out,
it translates to an extra newline going to the next-next line.
This spoils the behavior of programs which depend on the VT100
behavior.

In this patch, the VT100 behavior is simulated as follows. A
new flag in the dev_console structure is set when a character
is output to the last column. This flag is then observed in
order to discard a newline (or rather any character which is
mapped mapped to the DWN action).

* winsup/cygwin/fhandler.h (class dev_console): New boolean
data member, eat_newline. This indicates that if a character
is output which moves down to the next line, it should be
discarded rather than sent to the console.

* winsup/cygwin/fhandler_console.cc
(fhandler_console::write_normal): Set the eat_newline flag
if the text output ends up at column zero. Honor the
eat_newline flag when processing a DWN character, and clear
it when processing certain other control characters.

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