Revert "Skip .copy(order=...) tests for numpy <1.6, which cannot handle it"

This reverts commit 7aca3a50139ed324a9bd082c7a1b92ffdd3665c8.

Conflicts:
	astropy/units/tests/test_quantity.py
Revert "Remove Quantity.copy() as the ndarray version is fine; add tests for order"

This reverts commit 71e6ee36b4302b34ada7621ce69199f7029f0d8d.

Conflicts:
	astropy/units/tests/test_quantity.py