gitk: Bind Key-Return to create on new branch dialog

The Return key can now be used as well as pressing the Create button
from the dialog box that is shown when selecting "Create new branch".

Signed-off-by: Richard Quirk <richard.quirk@gmail.com>
Signed-off-by: Paul Mackerras <paulus@samba.org>

gitk

@@ -7625,6 +7625,7 @@ proc mkbranch {} {
     grid $top.id $top.sha1 -sticky w
     label $top.nlab -text [mc "Name:"]
     entry $top.name -width 40
+    bind $top.name <Key-Return> "[list mkbrgo $top]"
     grid $top.nlab $top.name -sticky w
     frame $top.buts
     button $top.buts.go -text [mc "Create"] -command [list mkbrgo $top]