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/FiniteElementMethod/OpenTissue/utility/utility_empty_traits.h

@@ -0,0 +1,30 @@
+#ifndef OPENTISSUE_UTILITY_UTILITY_EMPTY_TRAITS_H
+#define OPENTISSUE_UTILITY_UTILITY_EMPTY_TRAITS_H
+//
+// OpenTissue Template Library
+// - A generic toolbox for physics-based modeling and simulation.
+// Copyright (C) 2008 Department of Computer Science, University of Copenhagen.
+//
+// OTTL is licensed under zlib: http://opensource.org/licenses/zlib-license.php
+//
+
+namespace OpenTissue
+{
+  namespace utility
+  {
+    /**
+    * Empty Traits Class.
+    * This is basically an empty class it usage
+    * is intended as a default argument for the
+    * many algorithms and data structures where
+    * the default traits is simply the ``empty''
+    * traits.
+    *
+    */
+    class EmptyTraits { };
+
+  }
+}
+
+// OPENTISSUE_UTILITY_UTILITY_EMPTY_TRAITS_H
+#endif