append more commands for git-gui

git-gui.tcl

    $ctxm add command -label [mc "Open in external editor"] \
		-command {
            #set prog "notepad"
            set prog "C:\\Program Files (x86)\\Notepad++\\notepad++.exe"
            exec $prog [file join $_gitworktree $current_diff_path]
        }
    $ctxm add command -label [mc "Reset file changes"] \
        -command {
            if { $current_diff_path ne "" && [tk_messageBox \
                -icon question \
                -type yesno \
                -default no \
                -title "[appname]: Question" \
                -message [mc "Restore the most recent version of this file?"]] eq {yes}} {
                git "checkout" $current_diff_path
                ui_do_rescan
            }
        }