MAINT: don't use open(.., 'U') in Python 3.x, is deprecated.

This is default behavior in 3.x; in 2.x open() doesn't have a `newline`
kw.  So make code Python-version-specific.
TST: fix test failure due to comparing floats with assert_equal.

Observed on 32-bit linux with python 3.4b1
DOC: update release notes with new fixes since rc1