fixing bug in missing value handeling, wasn't picking up 'F' columns.
fixing bug in missing value handeling, wasn't picking up 'F' columns.

Alwnikrotikz/pysal,AlanZatarain/pysal,AlanZatarain/pysal,Alwnikrotikz/pysal,tectronics/pysal,tectronics/pysal,tectronics/pysal,Alwnikrotikz/pysal,AlanZatarain/pysal