gets: Return (None, None) when key does not exist

[pawelkowalak]

This changes behavior of gets command to be compatible with get command.

[lericson]

Needs a test

[lericson]

This is an API change and should be documented as such, it'll be in 1.3.0 since it's pretty harmless.

Out of curiosity, does this make the usage pattern any better or is it just purely out of aesthetic preference?

[pawelkowalak]

In our production system we're using libmemcached 0.49 and pylibmc from commit 16d50. That combination returned (None, None) tuple when calling gets() on non-existing key. After upgrading to pylibmc from HEAD and libmemcahced to 1.0.X we've noticed exceptions instead of (None, None). So in my opinion this change brings us back to original behavior of gets(), but I haven't investigated what caused that change.

[lericson]

Oh, okay. Should've been in 1.2.3 then, it's too far along now though.