Thanks, Rasmus! I'll review soon.

Merged, thanks.

Thanks @krakjoe!

The iscntrl -> !isgraph is a pretty major change, memcache protocol does support non-ascii keys as outlined in https://github.com/memcached/memcached/blob/master/doc/protocol.txt by implicit statements such as:

The value of keys (and potentially other things) are "URI encoded". Since most
keys used conform to standard ASCII, this should have no effect. For keys with
less standard or binary characters, "%NN"'s are inserted to represent the
byte, ie: "n%2Cfoo" for "n,foo".

and the general key protocol definition:

Keys

Data stored by memcached is identified with the help of a key. A key
is a text string which should uniquely identify the data for clients
that are interested in storing and retrieving it. Currently the
length limit of a key is set at 250 characters (of course, normally
clients wouldn't need to use such long keys); the key must not include
control characters or whitespace.

Commented in #546