evaluate: handle binop adjustment recursively

evaluate: handle binop adjustment recursively

currently this is fine, but a followup commit will add
EXPR_SET_ELEM handling.

And unlike RANGE we cannot assume the key is a value.
Therefore make binop_can_transfer and binop_transfer_one handle
right hand recursively if needed.  For RANGE, call it again with
from/to.

For future SET_ELEM, we can then just call the function recursively
again with right->key as new RHS.

Signed-off-by: Florian Westphal <fw@strlen.de>