modified search for libpng + added arch spec

 on osx libpng is installed in a non standard directory
 (/usr/X11) the png package included in cmake takes care
 of this.
 Additionally fltk currently has to be built as 386 on
 Snow Leopard, this then requires stage to be built as
 386 as well.
 This commit addopts the CMakeLists file to ensure the
 correct behavior with OSX Snow Leopard.
Merge branch 'master' of https://github.com/rtv/Stage

Conflicts:
	CMakeLists.txt
 added a Run method to World, reimplemented stest

 - added a new Run method to world, this way GUI/non-GUI
   world simulations can be started the same way.

 - reimplemented the libstage standalone test program.
   Since I'm not the original author, I'm not quite
   sure whether the behavior is the same as before.
debugging
fixed race condition caused by cached SR lookup
faster debug viz - occupancy and voxels
removed memset(p,0,sizeof(p)) of objects.
bail out more quickly when failing to load textures
Merge pull request #16 from mani-monaj/master

Add leading zeros to Stage generated screenshot file names.
Merge pull request #9 from chmp/master

New method World::Run, reimplemented stest
coloured walle model and added walle & fancy pioneer example
removed unused model_props file and folded model_getset and model_load into model.cc.

for faster builds and fewer things
added support for load/save of visualization options
started release notes for next release (4.1.0)
started release notes for next release (4.1.0)
*much* faster flag drawing
removed redundant triangles from flag drawing
added missing Color::GLSet() method
DW work
DW tweaks