Add rockbox fnt font; remove compiling warning
image: fix ARGB png randering

Initial patch provided by limxuzheng.

Github-hook: fix #43
topwin: fix a regression in fcda3a5f887

When we have multiple window tree and the parent is clipped by others,
activate child window don't get the parent to be repainted. Define
RTGUI_ONLY_ONE_WINDOW_TREE if your application only have one window tree
so we could do some optimization.

Conflicts:

	components/rtgui/server/topwin.c
topwin: use postorder traversal in _rtgui_topwin_draw_tree