Convert to float for comparison with float in IFDRational __eq__

[radarhere]

This one is up for debate.

Consider this behaviour.

>>> 7 / 5
1.4
>>> from PIL.TiffImagePlugin import IFDRational
>>> IFDRational(7, 5) == 1.4
False

I feel like this is unexpected. Why is this happening? Well,

>>> IFDRational(7, 5)._val
Fraction(7, 5)
>>> from fractions import Fraction
>>> Fraction(7, 5) == 1.4
False

So despite the fact that

>>> float(Fraction(7, 5)) == 1.4
True

Fraction(7, 5) is not equal to 1.4.

This isn't the case for all values.

>>> Fraction(5, 4) == 1.25
True

This PR 'fixes' this behaviour in IFDRational by casting Fraction to float when comparing in IFDRational.__eq__().

As I said, open for debate.