In python3 np.test would raise an error if raise_warnings is a list
since dict.keys() now returns a dict_keys instance. Eg,

    np.test('full', raise_warnings=[FutureWarning])

TST: Make default for all warnings "always"

function listed in __all__ for numpy/testing/utils.py.

This should make it easier in some cases, since a warning
caught in some test (but not important/not causing failure),
will not shadow later tests.
In principle the best thing is probably to always check the number
of warnings raised, so that you notice when a new warning shows
up in a test, though there may be other corner cases here.

Filed upstream as:
    https://github.com/nose-devs/nose/issues/929
Not our problem.

The ndarray richcompare function has special case code for handling
void dtypes (esp. structured dtypes), since there are no ufuncs for
this. Previously, we would attempt to call the relevant
ufunc (e.g. np.equal), and then when this failed (as signaled by the
ufunc returning NotImplemented), we would fall back on the special
case code. This commit moves the special case code to before the
regular code, so that it no longer requires ufuncs to return
NotImplemented.

Technically, it is possible to define ufunc loops for void dtypes
using PyUFunc_RegisterLoopForDescr, so technically I think this commit
changes behaviour: if someone had registered a ufunc loop for one of
these operations, then previously it might have been found and
pre-empted the special case fallback code; now, we use the
special-case code without even checking for any ufunc. But the only
possible use of this functionality would have been if someone wanted
to redefine what == or != meant for a particular structured dtype --
like, they decided that equality for 2-tuples of float32's should be
different from the obvious thing. This does not seem like an important
capability to preserve.

There were also several cases here where on error, an array comparison
would return a scalar instead of raising. This is supposedly
deprecated, but there were call paths that did this that had no
deprecation warning. I added those warnings.

Add context manager for tests that, on entry, clears record of any
previous warnings from given modules, so that any warning raised in the
context block does get raised, rather than suppressed by a previous
warning causing an entry in the `__warningregistry_`` of the module.

Fixed typos in docstrings were updated for functions where the parameter
names in the docstring didn't match the function signature.