BUG: fix string type inconsistency between zeros and zeros_like

np.zeros for strings returns empty strings while np.zeros_like of a
string array creates strings containing an string 0.
BUG: Avoid type promotion in tril and triu.
Merge pull request #4917 from juliantaylor/zeros_like_string

BUG: fix string type inconsistency between zeros and zeros_like
Merge pull request #4916 from yotam/triu-dtype-fix

BUG: Avoid type promotion in tril and triu.
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.
MAINT: Fix problems noted by pyflakes in numpy/lib/tests.
STY: PEP8 compliance for numpy/lib/tests.

The possibly controversial part of this is making the nested array
value lists PEP8 compliant, as there is something to be said aligning
the values for clarity. In the end, it seemed like the easiest thing
to do was to make them PEP8 compliant. The eye can get used to that.
MAINT: Fixes for problems in numpy/lib revealed by pyflakes.

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.
STY: Make files in numpy/lib PEP8 compliant.

The rules enforced are the same as those used for scipy.
Merge pull request #4929 from juliantaylor/charris-pep8-numpy-lib

Charris pep8 numpy lib
DOC: matrix flatten docstring
DOC: use m for matrix instead of a for array
DOC: clarify matrix flatten docstring
DOC: add minimal clarification to the matrix.ravel docstring
MAINT: fix the import