Fix undefined names in Python code (#99)

* Fix undefined names in Python code

* revert four files

Author: cclauss

demo/_curses.py

@@ -5,6 +5,11 @@
 
 from _curses_cffi import ffi, lib
 
+try:
+    unicode
+except NameError:
+    unicode = str
+
 
 def _copy_to_globals(name):
     globals()[name] = getattr(lib, name)

demo/bsdopendirtype.py

@@ -1,3 +1,4 @@
+import os
 from _bsdopendirtype import ffi, lib
 
 

demo/recopendirtype.py

@@ -1,3 +1,4 @@
+import os
 from _recopendirtype import ffi, lib