The memcached statistics code is pretty old, and has a lot of warts. One

of those warts is that hostnames without ports would lead to crashes,

and another is that "STAT" lines containing a name but not a value would

as well. A third is that we had to use the Django memcached backend to

get memcached stats.
This change fixes those three issues, and updates some of the syntax and

docs for the file.
The stats code is still very limited (other backends can't provide

stats, and we're assuming a lot about the data), but this will be

addressed separately.

Tested all the failure conditions I previously hit (lack of port causing

a crash, lack of value in a "STAT" line, and lack of stats for a custom

memcached backend).
Unit tests were not added, due to a planned redesign, which the tests

would not survive.