First pass of load files through an interface (to allow loading from memory, zip file etc). So instead of posix fopen/fread, using CommonFileIOInterface.

A fileIO plugin can override custom file IO operations. As a small test, load files from a zipfile in memory.
Default fileIO implementation is in examples/Utils/b3BulletDefaultFileIO.h
Affects URDF, SDF, MJCF, Wavefront OBJ, STL, DAE, images.

examples/Importers/ImportSDFDemo/ImportSDFSetup.cpp

@@ -162,7 +162,7 @@ void ImportSDFSetup::initPhysics()
 
 	m_dynamicsWorld->setGravity(gravity);
 
-	BulletURDFImporter u2b(m_guiHelper, 0, 1, 0);
+	BulletURDFImporter u2b(m_guiHelper, 0, 0, 1, 0);
 
 	bool loadOk = u2b.loadSDF(m_fileName);