doctest assumed that a package's __loader__.get_data() method used universal
newlines; it doesn't.  To rectify this the string returned replaces all
instances of os.linesep with '\n' to fake universal newline support.

Backport candidate.
diff --git a/Lib/test/test_doctest.py b/Lib/test/test_doctest.py
index e2a24c4..e96785c 100644
--- a/Lib/test/test_doctest.py
+++ b/Lib/test/test_doctest.py
@@ -1908,6 +1908,23 @@
          >>> suite.run(unittest.TestResult())
          <unittest.TestResult run=3 errors=0 failures=3>
 
+       Support for using a package's __loader__.get_data() is also
+       provided.
+
+         >>> import unittest, pkgutil, test
+         >>> if not hasattr(test, '__loader__'):
+         ...     test.__loader__ = pkgutil.get_loader(test)
+         ...     added_loader = True
+         >>> try:
+         ...     suite = doctest.DocFileSuite('test_doctest.txt',
+         ...                                  'test_doctest2.txt',
+         ...                                  'test_doctest4.txt',
+         ...                                  package='test')
+         ...     suite.run(unittest.TestResult())
+         ... finally:
+         ...     del test.__loader__
+         <unittest.TestResult run=3 errors=0 failures=3>
+
        '/' should be used as a path separator.  It will be converted
        to a native separator at run time: