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.
Fixed indentation of example in tutuorial 2.
Removed import * in tests.

Thanks to flake8 path/to/file.py | awk -F ' ' '{ print $5 }' | sort | uniq
Fixed #5789 -- Changed LocaleMiddleware session variable to '_language'.

The old 'django_language' variable will still be read from in order
to migrate users. The backwards-compatability shim will be removed in
Django 1.8.

Thanks to jdunck for the report and stugots for the initial patch.
Fixed E221 pep8 warnings.
Fixed #17027 -- Added support for the power operator in F expressions.

Thanks dan at dlo.me for the initial patch.

- Added __pow__ and __rpow__ to ExpressionNode
- Added oracle and mysql specific power expressions
- Added used-defined power function for sqlite
Fixed #21304 -- Typo in docs/topics/testing/advanced.txt

Thanks joao at silvaneves.org for the report.
Added 1.5.5 and 1.4.9 release notes
Fixed #21307 -- Moved TransRealMixin to django.test.utils.
Fixed E225 pep8 warnings.
Workaround admin scripts test failures on Windows+Python 3.

Change strategy used to examine instrumented output to acommodate the
fact that on Windows, where the path separator is '\', repr() of Python
modules has changed in Python 3 to use escaped backslashes in the FS
path section (e.g.
'C:\\python3x\\Lib\\site-packages\\django\\contrib\\auth\\models.py')
without having to special-case based on platform.
Fixed #13245: Explained Oracle's behavior w.r.t db_table
and how to prevent table-name truncation

Thanks russellm & timo for discussion, and timo for review.
Fixed #21298 -- Fixed E301 pep8 warnings
typo on 1.7 release notes
Merge pull request #1801 from collinanderson/patch-10

typo in 1.7 release notes
Fixed #12027 -- Fixed EmailValidator to reject a trailing dot.

Thanks Klas H for the report and claudep for the patch.
Fix migration planner to fully understand squashed migrations. And test.
Fixed #19941 -- Removed sys.path hack when running the test suite.

Thanks jezdez for the suggestion.
Bumped release date for 1.5.5 & 1.4.9.
Fixed #20945 -- Allowed cache tag to use a specific cache.