[issue23591] enum: Add Flags and IntFlags

[STINNER Victor]

STINNER Victor added the comment:

As noticed by veky on the review, _high_bit() is slow and can be optimized using int.bit_length(). Attached bit_length.patch implements this.

_high_bit(0) returns -1. Maybe an exception must be raised if the argument is < 1? (also fail for negative number)

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Added file: http://bugs.python.org/file44319/bit_length.patch

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