Fix coverage config and master_len test

Something has changed in pytest (or something to do with the test
suite). All of a sudden some warnings are getting suppressed within a
function despite setup_module supposedly activating warnings always.

coverage.cfg

@@ -1,9 +1,9 @@
 [run]
 branch = True
-include = compoundfiles/*
-;omit = */bar.py,*/baz.py
+source = compoundfiles
 
 [report]
+include = compoundfiles/*
 ignore_errors = True
 show_missing = True
 exclude_lines =

tests/test_function.py

@@ -39,7 +39,7 @@
 
 DirEntry = namedtuple('DirEntry', ('name', 'isfile', 'size'))
 
-def setup_module(module):
+def setup_function(fn):
     warnings.simplefilter('always')
 
 def verify_contents(doc, contents):
@@ -461,7 +461,7 @@ def test_strange_master_ext():
 def test_invalid_master_loop():
     with pytest.raises(cf.CompoundFileMasterLoopError):
         # Same as strange_master_ext.dat but with DIFAT extension sector filled
-        # and terminated with a self, test_contents=False-reference
+        # and terminated with a self-reference
         doc = cf.CompoundFileReader('tests/invalid_master_loop.dat')
 
 def test_invalid_master_len():