v2gitk: Add horizontal scrollbar to the diff view

> Adding horizontal scroll bar makes the scrolling feature more
> discoverable to the users. The horizontal scrollbar is a bit narrower
> than vertical ones so we don't make too big impact on available screen
> real estate.
>
> An interesting side effect of Tk scrollbars is that the "elevator"
> size changes depending on the visible content. So the horizontal
> scrollbar "elevator" changes as the user scrolls the view up and down.
>
> Signed-off-by: Pekka Kaitaniemi <kaitanie@cc.helsinki.fi>
> ---
> This patch adds a relatively narrow horizontal scrollbar to the diff
> pane. It might be a bit more complicated to implement an on-demand
> one, however...
>
> The patch seems to work fine on Linux and ion3 window manager. I
> haven't had a chance to test it with other systems.
>
>  gitk |    6 +++++-
>  1 files changed, 5 insertions(+), 1 deletions(-)
>
> diff --git a/gitk b/gitk
> index f1f21e9..5340811 100755
> --- a/gitk
> +++ b/gitk
> @@ -857,14 +857,18 @@ proc makewindow {} {
>      set ctext .bleft.ctext
>      text $ctext -background $bgcolor -foreground $fgcolor \
>  	-state disabled -font textfont \
> -	-yscrollcommand scrolltext -wrap none
> +	-yscrollcommand scrolltext  -wrap none \
> +	-xscrollcommand ".bleft.sbhorizontal set"
>      if {$have_tk85} {
>  	$ctext conf -tabstyle wordprocessor
>      }
>      scrollbar .bleft.sb -command "$ctext yview"
> +    scrollbar .bleft.sbhorizontal -command "$ctext xview" -orient h \
> +	-width 10
>      pack .bleft.top -side top -fill x
>      pack .bleft.mid -side top -fill x
>      pack .bleft.sb -side right -fill y
> +    pack .bleft.sbhorizontal -side bottom -fill x -in .bleft
>      pack $ctext -side left -fill both -expand 1
>      lappend bglist $ctext
>      lappend fglist $ctext
>   

> Pekka Kaitaniemi writes:
> 
> > -	-yscrollcommand scrolltext -wrap none
> > +	-yscrollcommand scrolltext  -wrap none \
> 
> Why this whitespace change?

> > +    scrollbar .bleft.sbhorizontal -command "$ctext xview" -orient h \
> > +	-width 10
> 
> Are you using Tk 8.4 or 8.5?  With Tk 8.5 the scrollbars are thinner
> and I wonder whether specifying a width of 10 will actually make it
> fatter than it would be otherwise.