potential memcached client incompatibility

[nerdvegas]

We have seen a potential memcached serialization issue recently, which may be an incompatibility introduced between memcached v1.53 and v1.59.

This is not the same issue, but shows that incompatibilities like this are possible: linsomniac/python-memcached#140

Symptom: On some occasions, package.py data has timestamp field as long rather than int, causing package serialization to fail. The problem goes away if memcached is disabled.

Suggestion: Add the memcached client version number to the keys used to write/read memcache, so that there is no overlap between different memcached clients (and by extension newer/older rez versions). This is easy to do and does not come at any cost.

I don't want to spend a lot of time digging into this issue, since a port to redis is on the cards anyway. I think there's a reasonable chance the fix suggested above will work.