Improved platform checking

Adding platform check to setup.py
Moving platform check in __init__.py as early as possible

Author: jstenar

pyreadline/__init__.py

@@ -7,14 +7,15 @@
 #  the file COPYING, distributed as part of this software.
 #*****************************************************************************
 from __future__ import print_function, unicode_literals, absolute_import
-
-from . import unicode_helper
-from . import logger, clipboard, lineeditor, modes, console
-from . rlmain import *
 from platform import system
+
 _S = system()
 if 'windows' != _S.lower():
     raise RuntimeError('pyreadline is for Windows only, not {}.'.format(_S))
 del system, _S
 
+from . import unicode_helper
+from . import logger, clipboard, lineeditor, modes, console
+from . rlmain import *
+
 from . import rlmain

setup.py

@@ -12,6 +12,11 @@
 import sys
 import glob
 from distutils.core import setup
+from platform import system
+
+_S = system()
+if 'windows' != _S.lower():
+    raise RuntimeError('pyreadline is for Windows only, not {}.'.format(_S))
 
 # BEFORE importing distutils, remove MANIFEST. distutils doesn't properly
 # update it when the contents of directories change.