It has long been a minor annoyance that this isn't the
default behaviour. Semantics are as follows:
- Fees are calculated automatically, as usual, and shown
in black
- If the user inputs a fee, it is retained, and shown in
blue to indicate it is user-overridden
- The user can switch back to automatic fee calculation mode
in two ways: press Clear, or blank out the fee field
- User fees are also cleared by do_clear(), for instance when
the payment is sent
I have checked all usage combinations I could think of, including
the ! case, and all work in a sensible and natural fashion.
This also fixes issue #995.
aa6de86c27