update RT-Thread simulation on win32.
fixed compiling warning.
fixed finsh shell compiling warning.
added more example applications in realtouch demo.
fixed compiling warning and performed application code clean up.
fix comment typo
implement the top layer window

As we show/clip the windows tree from left to right, from bottom to top,
an always-on-top window is the window that should always be in left.
It's tricky but we could get the work done by changing little of code.
The diff is pretty small.

Create window with RTGUI_WIN_STYLE_ONTOP to let the window be in top
layer.
demo RTGUI_WIN_STYLE_ONTOP
Merge pull request #1 from grissiom/ltop

Implement top layer window
suppress the compiling cmd line by default

The cmd line of compliling is lenghty and there is no need to see them
in most of the cases. Suppress them will make warnings more clearer to
see. However, SCons 2.1.0 has a bug on LINKCOMSTR on VC tools. So the
LINKCOMSTR doesn't work.

If you want to see the full cmd line output, use `scons.bat VERBOSE=1`.
fix a bug that normal window will clip top layer window
name the topwin.flag enum
simplify the desktop window implementation

By this commit, the window Z-tree has split into 3 region: top layer,
middle layer and bottom layer. Former desktop window should be "bottom
layer window" which is always beneath the top and middle layer windows.
While getting more powerful and flexible(the bottom is a layer now and
we could have multiple bottom windows even only one is enough for most
of the cases), this implementation is simpler then the previous one.
update desktop testcase
add event_set_wm to rtgui_event_generic
remove wrong assert in rtgui_combobox_pdwin_onite
we don't have rtgui_app_{show,hide}
PNG add alpha in the rtgui_image_png_blit function.
the alpha formula: output = alpha * foreground + (1-alpha) * background
Signed-off-by: amsl <iamyhe@gmail.com>
Merge pull request #2 from grissiom/ndesktop

New desktop implementation
when hide/remove windows, activate next window in the same layer