BUG: Fix typo in hermite_e.py.

The hermepow function was incorrectly listed in __all__ as hermpow.
STY: PEP8 fixes for files in numpy/polynomial.

The rather lax standards used in scipy were used to identify the
needed style fixups.
MAINT: Remove unused variables and imports in numpy/polynomial/*.py.

Detected by pyflakes.
STY: PEP8 fixes for numpy/polynomial/tests/*.py.

Made conformant with the standards of scipy.
MAINT: Fix blemishes in numpy/polynomial/tests revealed by pyflakes.
ENH: better error message for invalid axis and concatenate inputs

the old errors
np.concatenate(1,2)
TypeError: object of type 'int' has no len()

concatenate([1], [2])
TypeError: an integer is required

are not very unhelpful, add a new internal function that allows adding
some context to axis argument conversion failures and check for sequence
inputs in concatenate.
Closes gh-4923.
DOC: add minimal clarification to the matrix.ravel docstring
MAINT: fix the import
MAINT: restore optional ravel order and add tests and more docstring lines
DOC: clarify that matrix.ravel only copies if necessary; this is already tested
DOC: Fix typo in _iotools.py docstring.

The error is in the StringConverter.upgrade docstring.
DOC: matrix.squeeze docstring
Merge pull request #4943 from argriffing/matrix-squeeze-docs

DOC: matrix.squeeze docstring
MAINT: small change to squeeze error message
MAINT: use N.ndarray instead of core.multiarray.ndarray
Merge pull request #4946 from argriffing/squeeze-bad-axis-size

MAINT: small change to squeeze error message
Merge pull request #4932 from argriffing/ravel-docstrings

DOC: clarify matrix.ravel docstring and add tests
Merge pull request #4924 from charris/pep8-numpy-polynomial

Pep8 numpy polynomial
Merge pull request #4938 from charris/fix-docstring-typo

DOC: Fix typo in _iotools.py docstring.
Merge pull request #4926 from juliantaylor/concatenate-error

ENH: better error message for invalid axis and concatenate inputs