[patch] PL/Python is too lossy with floats

PL/Python uses str(v) to convert float data, but is lossy
by design. Only repr(v) is guaranteed to have enough
precision to make floats roundtrip properly:

https://docs.python.org/2/library/functions.html#func-repr
https://docs.python.org/2/library/functions.html#str

Example:

$ python
>>> repr(100100100.654321)
'100100100.654321'
>>> str(100100100.654321)
'100100100.654'

Attached patch uses PyObject_Repr() for float data.

As it's annoying-to-debug problem and the patch is simple,
perhaps it's worth backporting?

--
marko