Common prefixes break `alces about` command

[benarmston]

If there are two "alces about topics" where one is a prefix of the other, it is not possible to view them both.

Consider there are two topics, say www and www-api. Running alces about www-api will show the output for the www-api topic. However, running alces about www will show

alces about: ambiguous selection: www
Did you mean one of these?
    www
    www-api