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.
Merge pull request #4924 from charris/pep8-numpy-polynomial

Pep8 numpy polynomial