Xlocale

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- More Python 3 compilation fixes.

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- Python 3 has no PyInt.

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- Fix handling of exceptions raised when creating a Locale: they are now
correctly seen as being raised in the constructor.

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- Add Python 3 support.
- Add manylinux support.

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- No longer return the current locale from Locale.use(). This created
unsolvable double free problems.

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- Fix a memory handling error in Locale.use() which could result in a segfault
when using a locale instance multiple times.