New in version 1.1.
True when rational is of the form 1/2**n. Otherwise false:
abjad> from abjad.tools import durationtools
abjad> for n in range(1, 17): # doctest: +SKIP
... rational = Fraction(1, n)
... print '%s\t%s' % (rational, durationtools.is_binary_rational(rational))
...
1 True
1/2 True
1/3 False
1/4 True
1/5 False
1/6 False
1/7 False
1/8 True
1/9 False
1/10 False
1/11 False
1/12 False
1/13 False
1/14 False
1/15 False
1/16 True
Return boolean.