Fix performance regression with per-file-ignores

With a large number of errors, filenames, and per-file-ignores the style guide
selection would take a significant portion of execution time
(python3 70% / python2 99.9%).

Caching the styleguide lookup by filename eliminates this bottleneck.

1 files changed, 1 insertions, 1 deletions

diff --git a/setup.py b/setup.py
index f723716..088de25 100644
--- a/setup.py
+++ b/setup.py
@@ -28,7 +28,7 @@ requires = [
 extras_require = {
     ":python_version<'3.4'": ['enum34'],
     ":python_version<'3.5'": ['typing'],
-    ":python_version<'3.2'": ['configparser'],
+    ":python_version<'3.2'": ['configparser', 'functools32'],
 }
 
 if int(setuptools.__version__.split('.')[0]) < 18: