BUG: test_fortran_order_buffer fails on big endian architectures.

The numpy unicode string comparison function does not work correctly
for non-native byte orders. That is a problem needing fixing, but
test_fortran_order_buffer is only needed to check that the buffer
works correctly for fortran order buffers, so let the endianess of
test data be the platform default.
Merge pull request #3941 from charris/make-test-endian-independent

BUG: test_fortran_order_buffer fails on big endian architectures.