Confusing wording in documentation

[johto]

Hi,

Commit 449d2b3 added some wording to the documentation I find very confusing. It's this part:

Starting with B<memcached> 1.3.3 I<$key> should be set to a number or the command will fail.

Surely what we meant instead is that $key should be set to the key of a number stored in memcached -- or in other words that the corresponding key in memcached should be set to a number.