Update numpy tests

Extra tests for NumPy support #549 

Added tests for a bunch of functions in NumPy (most of them under "Floating Functions".

Also reordered tests to follow the same order in tests to that in the listing of the ufuncs in "numpy_support.rst", that is itself based on the ufunc documentation in NumPy:
http://docs.scipy.org/doc/numpy/reference/ufuncs.html (see under Available functions):

Note that the following functions appear as "ufuncs" under that documentation, but actually aren't ufuncs:
ones_like
isreal
iscomplex

Overall, these tests need some refactoring (probably some splitting would make them more manageable).
More thought test cases and the ability to test ldexp (the limited binary tests cannot be applied to it, as ldexp
requires the second argument to be an integer).

I've introduced back some "expectedFailures" for "no-python" tests for functions that are not yet supported.
In order to make the semantics evident, I've used "_unimplemented" that maps to unittest.expectedFailure.
As we increase coverage of NumPy ufuncs in no-python mode those will disappear.
It doesn't seem you're skipping anything. Is this variable still useful?