Account for Embedded String Encoding when calculating memory used by a key

[sripathikrishnan]

Antirez has a new memory optimization branch - redis/redis@unstable...memopt

Smaller strings (less than 32 bytes) are inlined. This gets rid of an extra pointer, and so saves some memory (not a whole lot). Not a big deal, but something that we should account never the less.

This should be fixed only after the optimization branch reaches unstable/master branch.