(滚动条的使用)

在P124程序sysmets2.c基础上，完成如下功能：

1)　　仿照垂直滚动条功能的实现，使窗口具有水平滚动条

2)　　能够响应滚动条消息：

SB_LINEUP、SB_LINELEFT、 SB_LINEDOWN、SB_LINERIGHT、　　 　　　　 SB_PAGEUP、SB_PAGELEFT、SB_PAGEDOWN、SB_PAGERIGHT、SB_THUMBTRACK、SB_TOP、 SB_LEFT、SB_BOTTOM、SB_RIGHT； -(Using the scroll bar) in the P124 program sysmets2.c on the basis of the following functions: 1) modeled on the vertical scroll bar to achieve functional, so the window has a horizontal scroll bar 2) to respond to the scroll bar message: SB_LINEUP, SB_LINELEFT, SB_LINEDOWN, SB_LINERIGHT , SB_PAGEUP, SB_PAGELEFT, SB_PAGEDOWN, SB_PAGERIGHT, SB_THUMBTRACK, SB_TOP, SB_LEFT, SB_BOTTOM, SB_RIGHT