git-gui: add horizontal scrollbar to commit buffer

While the commit message widget has a configurable fixed width, it
nevertheless allowed to write commit messages which exceeded this limit.
Though there is no visual clue, that there is scrolling going on. Now
there is a horizontal scrollbar.

There seems to be a bug in at least Tcl/Tk up to version 8.6.8, which
does not update the horizontal scrollbar if one removes the whole
content at once.

Suggested-by: Birger Skogeng Pedersen <[email protected]>
Signed-off-by: Bert Wesarg <[email protected]>
Signed-off-by: Pratyush Yadav <[email protected]>

Author: bertwesarg

git-gui.sh

@@ -3363,10 +3363,16 @@ ttext $ui_comm -background white -foreground black \
 	-relief sunken \
 	-width $repo_config(gui.commitmsgwidth) -height 9 -wrap none \
 	-font font_diff \
+	-xscrollcommand {.vpane.lower.commarea.buffer.frame.sbx set} \
 	-yscrollcommand {.vpane.lower.commarea.buffer.frame.sby set}
+${NS}::scrollbar .vpane.lower.commarea.buffer.frame.sbx \
+	-orient horizontal \
+	-command [list $ui_comm xview]
 ${NS}::scrollbar .vpane.lower.commarea.buffer.frame.sby \
+	-orient vertical \
 	-command [list $ui_comm yview]
 
+pack .vpane.lower.commarea.buffer.frame.sbx -side bottom -fill x
 pack .vpane.lower.commarea.buffer.frame.sby -side right -fill y
 pack $ui_comm -side left -fill y
 pack .vpane.lower.commarea.buffer.header -side top -fill x