FIX: hdfstore queries of the form where=[('date', '>=', datetime(2013,1,...
```
FIX: hdfstore queries of the form where=[('date', '>=', datetime(2013,1,1)), ('date', '<=', datetime(2014,1,1))] were broken
- modified Expr.parse_back_compat to check for tuples, in w, and unpack into w, op, value
- modified Expr.__init__ to modify the where list/tuple with the parsed result
```
