Fix StringConverter to avoid OverflowError in genfromtxt. Before, int(2**66) would work
(and return a ‘long’) but then np.array([2**66], dtype=np.integer) would not work and
return an OverflowError which would propagate to genfromtxt. This commit fixes this by
ensuring testing in advance whether an OverflowError will occur. In addition, this adds
an explicit np.int64 entry on systems where integer means int32. Values larger than
2**63-1 will be cast as float. This includes a regression test and adds an entry to the
release notes.

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

The function was useing `'u' in case_sensitive` to detect `upper`.
Make that more precise with `case_sensitive.startswith('u').

Raise ValueError if case_sensitive has unrecognized value.

numpy.lib._iotools.StringConverter.upgrade should have a return value

The error is in the StringConverter.upgrade docstring.

The rules enforced are the same as those used for scipy.

Some of those problems look like potential coding errors. In those
cases a Fixme comment was made and the offending code, usually an
unused variable, was commented out.

The unicode fixer strips the u from u'hi' and converts the unicode type
to str. The first won't work for Python 2 and instead we replace the u
prefix with the sixu function borrowed from the six compatibility
package. That function calls the unicode constructor with the
'unicode_escape' encoder so that the many tests using escaped unicode
characters like u'\u0900' will be handled correctly. That makes the
sixu function a bit different from the asunicode function currently in
numpy.compat and also provides a target that can be converted back to
the u prefix when support for Python 3.2 is dropped. Python 3.3
reintroduced the u prefix for compatibility.

The unicode fixer also replaces 'unicode' with 'str' as 'unicode' is no
longer a builtin in Python 3. For code compatibility, 'unicode' is
defined either as 'str' or 'unicode' in numpy.compat so that checks like

    if isinstance(x, unicode):
        ...

will work properly for all python versions.

Closes #3089.

2to3: Apply zip fixer.

In Python 3 zip returns an iterator instead of a list. Consequently, in
places where an iterator won't do it must be enclosed in list(...).
Lists instead of iterators are also used in array constructors as using
iterators there usually results in an object array containing an
iterator object.

Closes #3094