closes #1

refs !1
*changed the static variables to be common variables.
If one opens a lot of files, using thread local could be an alternative as long as the compiler supports it.

src/OpenMesh/Core/IO/reader/OFFReader.cc

@@ -192,8 +192,8 @@ _OFFReader_::read_ascii(std::istream& _in, BaseImporter& _bi, Options& _opt) con
   OpenMesh::Vec4f           c4f;
   BaseImporter::VHandles    vhandles;
   VertexHandle              vh;
-  static std::stringstream  stream;
-  static std::string        trash;
+  std::stringstream         stream;
+  std::string               trash;
 
   // read header line
   std::string header;