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_qhull.h

@@ -0,0 +1,45 @@
+#ifndef OPENTISSUE_UTILITY_UTILITY_QHULL_H
+#define OPENTISSUE_UTILITY_UTILITY_QHULL_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
+//
+#include <OpenTissue/configuration.h>
+
+  //////////////////////////////////////////////////////////////////
+  //
+  // This is a bit tricky, I cant just include qhull_a.h as
+  // QHull advices, because MVC complains about math.h which
+  // is included "indirectly by qhull_a.h
+  //
+  // Hopefully furture releases of QHull will allow me to
+  // just write:
+  //
+  //  extern "C"
+  //  {
+  //    #include <Qhull/qhull_a.h>
+  //  }
+  //
+#if defined(__cplusplus)
+  extern "C"
+  {
+#endif
+#include <stdio.h>
+#include <stdlib.h>
+#include <qhull/qhull.h>
+#include <qhull/mem.h>
+#include <qhull/qset.h>
+#include <qhull/geom.h>
+#include <qhull/merge.h>
+#include <qhull/poly.h>
+#include <qhull/io.h>
+#include <qhull/stat.h>
+#if defined(__cplusplus)
+  }
+#endif
+
+//OPENTISSUE_UTILITY_UTILITY_QHULL_H
+#endif