BUG: don't propagate subtypes from np.where

the C implementation cannot preserve subclass attributes, this needs a
python wrapper using indexing for subclasses.
closes gh-5095
BUG: check if object provides len() before trying to iterate it

some libraries want object arrays from objects that are iterable but
rely on not providing len() to get the right dtype from numpy.
closes gh-5100
BUG: check success of PyArray_DescrFromType in PyArray_InnerProduct

closes gh-5065
DOC: remove preservena reference from docstrings

preservena is not not implemented.
the putmask docstring is misleading, currently copyto is faster for
dense or sparse masks while putmask is faster for random masks.
[ci skip]
Merge pull request #5104 from juliantaylor/inner-fix

BUG: check success of PyArray_DescrFromType in PyArray_InnerProduct
Merge pull request #5105 from juliantaylor/where-no-subtype

BUG: don't propagate subtypes from np.where
Merge pull request #5106 from juliantaylor/sequence-fix

BUG: check if object provides len() before trying to iterate it
Merge pull request #5107 from juliantaylor/na-doc

DOC: remove preservena reference from docstrings