Let Quantity treat input with unit attributes more carefully.
Add test that equivalencies set in the context are respected
Add test for TypeError on encountering bad units; clarify exception text
Merge pull request #3051 from mhvk/quantity-input-with-unit-copy-is-false

Let Quantity treat input with unit attributes more carefully.
Fix #3108: Allow comparison of units and non-convertible-to-units
Add CHANGES entry