client fixes

See merge request !3

4f9a370c introduced a bug where the wrong return value was chosen for
skipped items.

drinks-only has not worked (ever?) and nobody has complained
"all" has no implementation

They're less important, not more important!

Don't report the door as being in error status just because it is zero priced

See merge request !4

Even if a user is in door, the fact that it is priced as zero means it
is always reported as being in error state, and it cannot be selected by
clients from the menu. Hack around this with strcmp.

Dispense door confirmation now will only triggered in interactive shell.

See merge request !2

Added an extra confirmation step for `dispense door`

See merge request !1