various utf8 compatibility fixes

- OBJ import/export now work with non utf8 paths. (all exporters and importers need changes like this)
- strip non utf8 chars from new ID blocks (also applies to renaming)
- set the file rename button to allow non-utf8 chars.

source/blender/python/intern/bpy_rna.c

@@ -233,7 +233,7 @@ static const char *py_safe_unicode_to_byte(PyObject *py_str, PyObject **coerce)
 	}
 }
 
-static PyObject *py_safe_byte_to_unicode(char *str)
+static PyObject *py_safe_byte_to_unicode(const char *str)
 {
 	PyObject *result= PyUnicode_FromString(str);
 	if(result) {