hgk: ignore ctrl-z as EOF on windows

Port a patch from gitk. Original description:

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 <[e-mail]>
Signed-off-by: Paul Mackerras <[e-mail]>

contrib/hgk

@@ -208,7 +208,7 b' proc getcommits {rargs} {'
 	exit 1
     }
     set leftover {}
-    fconfigure $commfd -blocking 0 -translation lf
+    fconfigure $commfd -blocking 0 -translation lf -eofchar {}
     fileevent $commfd readable [list getcommitlines $commfd]
     $canv delete all
     $canv create text 3 3 -anchor nw -text "Reading commits..." \