Close files properly when looking for markers.

This one kept pypy unhappy. As I did not find a fast, reliable and
platform-independent way to look for open files, there is no regression
test for the problem. On the other hand: pypy tests fail (even more)
miserably without this fix.

CHANGES.rst

@@ -22,6 +22,8 @@ Changelog for z3c.testsetup
 - Fix keyword parsing of methods: accept methods that accept no
   keyword parameters.
 
+- Close files properly when looking for marker strings.
+
 
 0.8.3 (2010-09-15)
 ==================

src/z3c/testsetup/util.py

@@ -99,7 +99,9 @@ def get_marker_from_file(marker, filepath):
      :<Tag>: <Value>
 
     """
-    return get_marker_from_string(marker, open(filepath, 'r').read())
+    with open(filepath) as fd:
+        return get_marker_from_string(marker, fd.read())
+    return None
 
 
 def warn(text):