fix open file leak

--HG--
extra : transplant_source : 7%EC%04%1F%89%F6%AA%8C%7Fl%B5D%DA%D5%CAF%B7%A70%0D

Cython/Compiler/Main.py

@@ -7,7 +7,7 @@ from __future__ import absolute_import
 import os
 import re
 import sys
-import codecs
+import io
 
 if sys.version_info[:2] < (2, 6) or (3, 0) <= sys.version_info[:2] < (3, 2):
     sys.stderr.write("Sorry, Cython requires Python 2.6+ or 3.2+, found %d.%d\n" % tuple(sys.version_info[:2]))
@@ -427,7 +427,8 @@ def run_pipeline(source, options, full_module_name=None, context=None):
         # By default, decide based on whether an html file already exists.
         html_filename = os.path.splitext(result.c_file)[0] + ".html"
         if os.path.exists(html_filename):
-            line = codecs.open(html_filename, "r", encoding="UTF-8").readline()
+            with io.open(html_filename, "r", encoding="UTF-8") as html_file:
+                line = html_file.readline()
                 if line.startswith(u'<!-- Generated by Cython'):
                     options.annotate = True