Caused all long longs to be required native only in memoryviews.
NPY_SIZEOF_LONG_LONG never existed, replace documentation with existing
NPY_SIZEOF_LONGLONG and code with a sizeof(npy_longlong).

late return triggers an assert with python3.4 in debug mode.
Closes gh-4138.

Observed on 32-bit linux with python 3.4b1

This is default behavior in 3.x; in 2.x open() doesn't have a `newline`
kw.  So make code Python-version-specific.

closes gh-4018

When Getitem of the lexsort sequence argument failed
this was not checked.

Closes gh-4123

When converting an array of strings to datetime64, a "NaT" occurring
in the input would cause all subsequent values to be converted to NaT.

dt == NPY_DATETIME_NAT is used as error condition, so initialize it to
something else.

Python 2.4 repair