Add `print_function` to all `from __future__ import ...` statements
and use the python3 print function syntax everywhere.

Closes #3078.

The new import `absolute_import` is added the `from __future__ import`
statement and The 2to3 `import` fixer is run to make the imports
compatible. There are several things that need to be dealt with to make
this work.

1) Files meant to be run as scripts run in a different environment than
files imported as part of a package, and so changes to those files need
to be skipped. The affected script files are:

    * all setup.py files
    * numpy/core/code_generators/generate_umath.py
    * numpy/core/code_generators/generate_numpy_api.py
    * numpy/core/code_generators/generate_ufunc_api.py

2) Some imported modules are not available as they are created during
the build process and consequently 2to3 is unable to handle them
correctly. Files that import those modules need a bit of extra work.
The affected files are:

    * core/__init__.py,
    * core/numeric.py,
    * core/_internal.py,
    * core/arrayprint.py,
    * core/fromnumeric.py,
    * numpy/__init__.py,
    * lib/npyio.py,
    * lib/function_base.py,
    * fft/fftpack.py,
    * random/__init__.py

Closes #3172

This should be harmless, as we already are division clean. However,
placement of this import takes some care. In the future a script
can be used to append new features without worry, at least until
such time as it exceeds a single line. Having that ability will
make it easier to deal with absolute imports and printing updates.

assert in non-testing files that should be checked for correctness.

Since CopyInto uses the dtype transfer mechanism to do the copying,
this also fully handles casting.  This also exposed a byte order issue
in the dtype transfer code of converting to object arrays.

The switch from position-based structure copying to name-based copying
required a small change to a masked array test as well.

* assert_equal : use assert_equal_array on records
* assert_array_compare : prevent the common mask to be back-propagated to the initial input arrays.
* assert_equal_array : use operator.__eq__ instead of ma.equal
* assert_equal_less: use operator.__less__ instead of ma.less

core:
* Fixed _check_fill_value for nested flexible types
* Add a ndtype option to _make_mask_descr
* Fixed mask_or for nested flexible types
* Fixed the printing of masked arrays w/ flexible types.

assert_array_compare : make sure that the comparison is performed on ndarrays, and make sure we use the np version of the comparison function.
core:
* Try not to touch the data in unary/binary ufuncs, (including inplace)