- 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/BaseProcess.h

@@ -60,7 +60,7 @@ class Importer;
  *  to provide additional information to other steps. This is primarily
  *  intended for cross-step optimizations.
  */
-class ASSIMP_API SharedPostProcessInfo
+class SharedPostProcessInfo
 {
 public:
 
@@ -211,7 +211,7 @@ private:
  * should be executed. If the function returns true, the class' Execute() 
  * function is called subsequently.
  */
-class ASSIMP_API BaseProcess 
+class ASSIMP_API_WINONLY BaseProcess 
 {
 	friend class Importer;