For clarity; infer-value was too vague. The old spelling remains
supported for compatibility, but is now deprecated.
When typing, --infer-market or even --infer (for now) is sufficient.
It seems to be convention to start the completion function name with an
underscore. I also prepend an underscore to the global variable.
(I still don't understand why env does not show this global variable
defined in the hledger-completion.bash script.)
