add btFileUtils::toLower to convert a string (char*) to lower case

URDF import demo: add COLLADA .dae file support
add FiniteElementMethod demo, extracted from the OpenTissue library (under the zlib license)
don't crash if loading an invalid STL file
add comparison with Assimp for COLLADA file loading (disabled by default, to avoid library dependency)
Gwen: disable some flags that make the build incompatible

Demos3/ImportSTLDemo/LoadMeshFromSTL.h

@@ -41,7 +41,15 @@ static GLInstanceGraphicsShape* LoadMeshFromSTL(const char* relativeFileName)
 					
 					if (numTriangles)
 					{
-						
+						{
+							//perform a sanity check instead of crashing on invalid triangles/STL files
+							int expectedBinaryFileSize = numTriangles* 50 + 84;
+							if (expectedBinaryFileSize != size)
+							{
+								return 0;
+							}
+
+						}
 						shape = new GLInstanceGraphicsShape;
 //						b3AlignedObjectArray<GLInstanceVertex>*	m_vertices;
 //						int				m_numvertices;