[1.6.x] Fixed an I18N test class tearDown method.

a3690168cb from master.
[1.6.x] Decode from UTF-8 explicitly when reading a text file in makemessages.

This shows itself with Python 3 under Windows where UTF-8 usually isn't
the default file I/O encoding and caused one failure and three errors
in our test suite under that platform setup.

b5f52647fe from master.