fix for setting numeric values.

With older underscore versions (tested with 1.5.2) _.size() for numeric
values throws TypeError. So _getValLength failed when setting numeric
values. With underscore 1.7.0 it works, as _.size() fallbacks to 0
there.
last commit broke TTL TEST. fixed that.
Merge pull request #17 from kaspars/master

fix for setting numeric values.