Disable --jobs on Windows

Fixes #164

flake8/engine.py

@@ -6,7 +6,7 @@ import pep8
 
 from flake8 import __version__
 from flake8.reporter import multiprocessing, BaseQReport, QueueReport
-from flake8.util import OrderedSet
+from flake8.util import OrderedSet, is_windows
 
 _flake8_noqa = re.compile(r'flake8[:=]\s*noqa', re.I).search
 
@@ -49,7 +49,7 @@ def get_parser():
         except ValueError:
             pass
 
-    if multiprocessing:
+    if multiprocessing and not is_windows():
         try:
             auto = multiprocessing.cpu_count() or 1
         except NotImplementedError:

flake8/util.py

@@ -1,4 +1,5 @@
 # -*- coding: utf-8 -*-
+import os
 
 try:
     import ast
@@ -43,6 +44,11 @@ def is_flag(val):
     return val.upper() in ('1', '0', 'F', 'T', 'TRUE', 'FALSE', 'ON', 'OFF')
 
 
+def is_windows():
+    """Determine if the system is Windows."""
+    return os.name == 'nt'
+
+
 def flag_on(val):
     """Return true if flag is on"""
     return str(val).upper() in ('1', 'T', 'TRUE', 'ON')