Make _to_own_unit aware of dtype of value coming in
Also ensure NaN are treated properly; add test cases
Speed up check if dtypes same; ensure numpy 1.5 does not fail
Changelog entry that quantity objects can be assigned NaN
Merge pull request #2695 from mhvk/quantity-do-not-prevent-recarray

Bug in Quantity.itemset for NaN values
Ensure in-place ops on Angles with non-angle result do not corrupt the instance