[PATCH] gitk: Ignore ctrl-z as EOF on windows

[PATCH] gitk: Ignore ctrl-z as EOF on windows

Cygwin's Tcl is configured to honor any occurence of ctrl-z as an
end-of-file marker, while some commits in the git repository and possibly
elsewhere include that character in the commit comment. This causes gitk
ignore commit history following such a comment and incorrect graphs. This
change affects only Windows as Tcl on other platforms already has
eofchar == {}. This fixes problems noted by me and by Ray Lehtiniemi, and
the fix was suggested by Shawn Pierce.

Signed-off-by: Mark Levedahl <mdl123@verizon.net>
Signed-off-by: Paul Mackerras <paulus@samba.org>