Copy bytes object when unpickling an array
Re-enable unpickling optimization for large py3k bytes objects.

Mutating a bytes object is theoretically unsafe, but doesn't cause any
problem in any existing version of CPython.
Merge pull request #371 from rlamy/bytes-pickle

Copy bytes object for small arrays when unpickling an array
FIX: Fixes the PyUnicodeObject problem in py-3.3

Previously NumPy did not compile in Python 3.3 due to the changes in PEP 393.
This patch simply calls PyUnicode_FromKindAndData() from the new Python 3.3 API
and possibly swaps the data before calling it if needed. The data in NumPy is always UCS4 and the PyUnicode_FromKindAndData() internally converts it to UCS1, UCS2 or UCS4 depending on the maximum code point.

The following tests now fail, because they produce invalid unicode in the
process (will be fixed in the next patch):

======================================================================
ERROR: Check byteorder of 0-dimensional objects
----------------------------------------------------------------------
Traceback (most recent call last):
  File "/home/ondrej/py33/lib/python3.3/site-packages/numpy/core/tests/test_unicode.py", line 277, in test_values0D
    self.assertTrue(ua[()] != ua2[()])
SystemError: invalid maximum character passed to PyUnicode_New

======================================================================
ERROR: Check byteorder of multi-dimensional objects
----------------------------------------------------------------------
Traceback (most recent call last):
  File "/home/ondrej/py33/lib/python3.3/site-packages/numpy/core/tests/test_unicode.py", line 297, in test_valuesMD
    self.assertTrue(ua[0,0,0] != ua2[0,0,0])
SystemError: invalid maximum character passed to PyUnicode_New

======================================================================
ERROR: Check byteorder of single-dimensional objects
----------------------------------------------------------------------
Traceback (most recent call last):
  File "/home/ondrej/py33/lib/python3.3/site-packages/numpy/core/tests/test_unicode.py", line 286, in test_valuesSD
    self.assertTrue(ua[0] != ua2[0])
SystemError: invalid maximum character passed to PyUnicode_New

======================================================================
ERROR: Check byteorder of 0-dimensional objects
----------------------------------------------------------------------
Traceback (most recent call last):
  File "/home/ondrej/py33/lib/python3.3/site-packages/numpy/core/tests/test_unicode.py", line 277, in test_values0D
    self.assertTrue(ua[()] != ua2[()])
SystemError: invalid maximum character passed to PyUnicode_New

======================================================================
ERROR: Check byteorder of multi-dimensional objects
----------------------------------------------------------------------
Traceback (most recent call last):
  File "/home/ondrej/py33/lib/python3.3/site-packages/numpy/core/tests/test_unicode.py", line 297, in test_valuesMD
    self.assertTrue(ua[0,0,0] != ua2[0,0,0])
SystemError: invalid maximum character passed to PyUnicode_New

======================================================================
ERROR: Check byteorder of single-dimensional objects
----------------------------------------------------------------------
Traceback (most recent call last):
  File "/home/ondrej/py33/lib/python3.3/site-packages/numpy/core/tests/test_unicode.py", line 286, in test_valuesSD
    self.assertTrue(ua[0] != ua2[0])
SystemError: invalid maximum character passed to PyUnicode_New
FIX: Make sure the tests produce valid unicode

The tests are testing byte order for unicode, so we can only use such unicode
data, so that both versions (swapped and unswapped) are valid unicode.