Also clean up its API slightly so that the caller passes in a name
describing the array being checked which is used to generate an error
message, rather than writing an error message from scratch.

This patch removes all direct assignments of non-NULL values to the
'base' field on PyArrayObjects. A new utility function was created to
set up UPDATEIFCOPY arrays, and all assignments to 'base' were
adjusted to use either PyArray_SetBaseObject or the new
PyArray_SetUpdateIfCopyBase.

One advantage of this is that it produces more consistent error
handling. This error handling revealed a bug in the nditer code,
which this patch does *not* yet fix.

The bug is that npyiter_new_temp_array sometimes (when dealing with
reversed axes) creates an array and then returns a view onto it. But,
npyiter_allocate_arrays assumes that the array returned by
npyiter_new_temp_array can have UPDATEIFCOPY set, which requires
reassigning its 'base' field. Previously, this meant that the
temporary array leaked. Now, it produces a ValueError.

This code path doesn't seem to actually be hit very often; only one of
the nditer tests fails because of the change. See
   numpy/core/tests/test_nditer.py:test_iter_array_cast_buggy

This is mostly a code cleanup, but it does have a user-visible effect
in that attempting to write to a unwriteable array now consistently
raises ValueError. (It used to randomly raise either ValueError or
RuntimeError.)

Passes numpy.test("full").

versioned

With the exception of the numarray fixups these were all instances
that were results of code generation.