- extract MaterialHelper and move all of its members to aiMaterial in /include.

- pull in IOhannes' patch to set the gcc default visibility for all symbols to NO and to mark ASSIMP_API with __attribute__ ((visibility("default"))).
- drop unneeded ASSIMP_API from most internal classes in /code, we just need to keep some exports on Windows to keep AssimpView alive.

git-svn-id: https://assimp.svn.sourceforge.net/svnroot/assimp/trunk@1066 67173fc5-114c-0410-ac8e-9d2fd5bffc1f

code/ScenePreprocessor.h

@@ -54,7 +54,7 @@ namespace Assimp	{
  *  importer, such as aiMesh::mPrimitiveTypes.
 */
 // ----------------------------------------------------------------------------------
-class ASSIMP_API ScenePreprocessor
+class ScenePreprocessor
 {
 	// Make ourselves a friend of the corresponding test unit.
 	friend class ::ScenePreprocessorTest;