Moved sys.path-extending decorator to django.test.utils and used throughout test suite.

Thanks Aymeric for the suggestion.

django/test/utils.py

@@ -526,3 +526,15 @@ class TransRealMixin(object):
 requires_tz_support = skipUnless(TZ_SUPPORT,
         "This test relies on the ability to run a program in an arbitrary "
         "time zone, but your operating system isn't able to do that.")
+
+
+
+@contextmanager
+def extend_sys_path(*paths):
+    """Context manager to temporarily add paths to sys.path."""
+    _orig_sys_path = sys.path[:]
+    sys.path.extend(paths)
+    try:
+        yield
+    finally:
+        sys.path = _orig_sys_path