gitk: Fix changing colors through Edit->Preferences

With tcl/tk8.5 the lset command seems to behave differently.  When
changing the background color through Edit->Preferences, the changes
are applied, but new dialogs, such as View->New view... barf with

 Error: unknown color name "{#ffffff}"

Additionally when closing gitk, and starting it up again, a bad value
has been saved to ~/.gitk, preventing gitk from running properly; it
fails with

 Error in startup script: unknown color name "{#ffffff}"
 ...

This commit fixes the problem by changing the color dialogs to pass
the empty string {} as the list index to choosecolor.  This causes
the lset and lindex commands used by choosecolor to use and set the
whole variable (bgcolor, fgcolor or selectbgcolor) rather than
treating them as a 1-element list.  Tested with tcl/tk8.4 and 8.5.

Dmitry Potapov reported this problem through
 http://bugs.debian.org/472615

Signed-off-by: Gerrit Pape <pape@smarden.org>
Signed-off-by: Paul Mackerras <paulus@samba.org>

gitk

@@ -8045,11 +8045,11 @@ proc doprefs {} {
     grid $top.cdisp - -sticky w -pady 10
     label $top.bg -padx 40 -relief sunk -background $bgcolor
     button $top.bgbut -text [mc "Background"] -font optionfont \
-	-command [list choosecolor bgcolor 0 $top.bg background setbg]
+	-command [list choosecolor bgcolor {} $top.bg background setbg]
     grid x $top.bgbut $top.bg -sticky w
     label $top.fg -padx 40 -relief sunk -background $fgcolor
     button $top.fgbut -text [mc "Foreground"] -font optionfont \
-	-command [list choosecolor fgcolor 0 $top.fg foreground setfg]
+	-command [list choosecolor fgcolor {} $top.fg foreground setfg]
     grid x $top.fgbut $top.fg -sticky w
     label $top.diffold -padx 40 -relief sunk -background [lindex $diffcolors 0]
     button $top.diffoldbut -text [mc "Diff: old lines"] -font optionfont \
@@ -8069,7 +8069,7 @@ proc doprefs {} {
     grid x $top.hunksepbut $top.hunksep -sticky w
     label $top.selbgsep -padx 40 -relief sunk -background $selectbgcolor
     button $top.selbgbut -text [mc "Select bg"] -font optionfont \
-	-command [list choosecolor selectbgcolor 0 $top.selbgsep background setselbg]
+	-command [list choosecolor selectbgcolor {} $top.selbgsep background setselbg]
     grid x $top.selbgbut $top.selbgsep -sticky w
 
     label $top.cfont -text [mc "Fonts: press to choose"]