When Angle is instantiated with Quantity, equivalence of unit ot radian must be checked.
Added Quantity to Angle conversion test cases.

Angle(1.0*u.deg) should be OK.
Angle(1.0*u.meter) should raise a UnitsError.
Angle(1.0*u.hour) should be converted to Angle(1.0, unit=u.hourangle).
Fix to allow Angle(1.0*u.hour)
Merge remote-tracking branch 'jwoillez/fix_quantity_to_angle' into unit/fix-identity
Don't create CompositeUnits unless necessary.  This restores the
behavior of "is" on irreducible units.  This also is a lot more
efficient, since creating and then simplifying composite units is
expensive.
Use copy rather than 1 * x -- might be faster
Reduce duplication of special 'hour' handling
Merge pull request #1714 from mdboom/unit/fix-identity

Quantity to Angle issue / Fix comparing irreducible units by identity