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/OBJReader.cc

@@ -172,7 +172,7 @@ read_material(std::fstream& _in)
   std::string keyWrd;
   std::string textureName;
 
-  static std::stringstream  stream;
+  std::stringstream  stream;
 
   std::string key;
   Material    mat;
@@ -308,7 +308,7 @@ read(std::istream& _in, BaseImporter& _bi, Options& _opt)
 
   std::string               matname;
 
-  static std::stringstream  stream, lineData, tmp;
+  std::stringstream         stream, lineData, tmp;
 
 
   // Options supplied by the user

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;

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

@@ -249,8 +249,8 @@ read_stla(std::istream& _in, BaseImporter& _bi, Options& _opt) const
 
   std::string line;
 
-  static std::string        garbage;
-  static std::stringstream  strstream;
+  std::string        garbage;
+  std::stringstream  strstream;
 
   bool facet_normal(false);