BUG: support data column indexers that have a large numbers of values

This is conceptually (and implemented) like an ``isin``

You can give a list of values that you want for a particular column, rather
than a boolean expression. This was already speced in the API, just
not implemented correctly!

Something like this
```
store.select('df',[pd.Term('users',[ 'a%03d' % i for i in xrange(60) ])])
```
originally from the mailing list
https://groups.google.com/forum/?fromgroups#!topic/pystatsmodels/oTjfOb0gazw