bug fix for str constr

Hi John, this is Zhen (Vaclav's intern). I noticed there was a bug in fancyq(-q :x, x: and ::) due to the incorrect use of the string constructor, which would generate a "pair string" of length 3 in some cases. That leads to a problem when saving the model and when using -q x:. Now it is fixed, sorry for the trouble and thank you!