- Fix http://sourceforge.net/projects/assimp/forums/forum/817654/topic/3591099.

- Add unit test to avoid ppfx-related issue with re-use of Importer's in future.
- X file loader now properly resets all of its members.
- OptimizeMeshes step now properly resets all of its member.
- Fix old (and already deprecated) makefile.mingw.

git-svn-id: https://assimp.svn.sourceforge.net/svnroot/assimp/trunk@593 67173fc5-114c-0410-ac8e-9d2fd5bffc1f

code/XFileImporter.cpp

@@ -96,6 +96,10 @@ void XFileImporter::InternReadFile( const std::string& pFile, aiScene* pScene, I
 	if( fileSize < 16)
 		throw new ImportErrorException( "XFile is too small.");
 
+	// need to clear members - this method might be called multiple
+	// times on a single XFileImporter instance.
+	mImportedMats.clear();
+
 	// in the hope that binary files will never start with a BOM ...
 	mBuffer.resize( fileSize);
 	file->Read( &mBuffer.front(), 1, fileSize);