Minor adjustments found during code review

changelog/4012.bugfix.rst

@@ -1 +0,0 @@
-``pytest.warn`` will capture previously-warned warnings in python2.  Previously they were never raised.

changelog/4102.bugfix.rst

@@ -0,0 +1 @@
+``pytest.warn`` will capture previously-warned warnings in Python 2. Previously they were never raised.

changelog/4102.feature.rst

@@ -1 +1,4 @@
 Reimplement ``pytest.deprecated_call`` using ``pytest.warns`` so it supports the ``match='...'`` keyword argument.
+
+This has the side effect that ``pytest.deprecated_call`` now raises ``pytest.fail.Exception`` instead
+of ``AssertionError``.

src/_pytest/recwarn.py

@@ -156,18 +156,18 @@ class WarningsRecorder(warnings.catch_warnings):
         if six.PY2:
 
             def warn(*args, **kwargs):
-                return self._warn(*args, **kwargs)
+                return self._saved_warn(*args, **kwargs)
 
-            warnings.warn, self._warn = warn, warnings.warn
+            warnings.warn, self._saved_warn = warn, warnings.warn
         return self
 
     def __exit__(self, *exc_info):
         if not self._entered:
             __tracebackhide__ = True
             raise RuntimeError("Cannot exit %r without entering first" % self)
-        # see above where `self.mp` is assigned
+        # see above where `self._saved_warn` is assigned
         if six.PY2:
-            warnings.warn = self._warn
+            warnings.warn = self._saved_warn
         super(WarningsRecorder, self).__exit__(*exc_info)