gitk: make sha1but a ttk::button

gitk's 'Commit ID' button uses a classic widget, not a themed one,
leading to inconsistent style. Commit 51a7e8b (d93f171 ("gitk: Use
themed tk widgets", 2009-04-17) that added themed widgets did not touch
this particular widget, but does not say why. Regardless, let's use a
themed button to be consistent with the rest of the interface.

Signed-off-by: Mark Levedahl <mlevedahl@gmail.com>

Author: mark987

gitk

@@ -2495,9 +2495,8 @@ proc makewindow {} {
     set sha1entry .tf.bar.sha1
     set entries $sha1entry
     set sha1but .tf.bar.sha1label
-    button $sha1but -text "[mc "Commit ID:"] " -state disabled -relief flat \
+    ttk::button $sha1but -text "[mc "Commit ID:"] " -state disabled \
         -command gotocommit -width 8
-    $sha1but conf -disabledforeground [$sha1but cget -foreground]
     pack .tf.bar.sha1label -side left
     ttk::entry $sha1entry -width $hashlength -font textfont -textvariable sha1string
     trace add variable sha1string write sha1change
@@ -8910,9 +8909,9 @@ proc sha1change {n1 n2 op} {
     }
     if {[$sha1but cget -state] == $state} return
     if {$state == "normal"} {
-        $sha1but conf -state normal -relief raised -text "[mc "Goto:"] "
+        $sha1but conf -state normal -text "[mc "Goto:"] "
     } else {
-        $sha1but conf -state disabled -relief flat -text "[mc "Commit ID:"] "
+        $sha1but conf -state disabled -text "[mc "Commit ID:"] "
     }
 }