io: force-interpret *.metadata as UTF-8 as otherwise unopenable on fr…

…_FR.UTF-8???

Fixes #1997

Orange/data/io.py

@@ -376,7 +376,7 @@ def write_table_metadata(cls, filename, data):
         if isinstance(filename, str) and hasattr(data, 'attributes'):
             if all(isinstance(key, str) and isinstance(value, str)
                    for key, value in data.attributes.items()):
-                with open(filename + '.metadata', 'w') as f:
+                with open(filename + '.metadata', 'w', encoding='utf-8') as f:
                     f.write("\n".join("{}: {}".format(*kv)
                                       for kv in data.attributes.items()))
             else:
@@ -392,7 +392,7 @@ def set_table_metadata(cls, filename, table):
                     table.attributes = pickle.load(f)
             # Unpickling throws different exceptions, not just UnpickleError
             except:
-                with open(filename + '.metadata') as f:
+                with open(filename + '.metadata', encoding='utf-8') as f:
                     table.attributes = OrderedDict(
                         (k.strip(), v.strip())
                         for k, v in (line.split(":", 1)