The manual said `a op= b` is equivalent to `a |= . op b`. It is actually
equivalent to `(b as $b | a |= . op $b)`: the right-hand side gets `.`
as input, not the value being updated, and each value it outputs gives a
separate result.
This updates the description and adds two examples, `.a += .b` and `.a
+= (1,2)`. `tests/man.test` and `jq.1.prebuilt` are regenerated.
Fixes#2119, fixes#2407
qodelicious
e440cccc0a