Adjust validator to IOError changes in Python 3.3
Adjust validator to IOError changes in Python 3.3

IOError is now just an alias of OSError, and functions now express the
actual problem that occurred using more specific subclasses. In
addition, Python 3 reports the relationship with previous exceptions
(exception chaining), making 'raise ... from ...' syntax appropriate in
some of the error messages.

mandawilson/cbioportal,angelicaochoa/cbioportal,zhx828/cbioportal,mandawilson/cbioportal,onursumer/cbioportal,cBioPortal/cbioportal,zhx828/cbioportal,onursumer/cbioportal,sheridancbio/cbioportal,n1zea144/cbioportal,mandawilson/cbioportal,zhx828/cbioportal,mandawilson/cbioportal,onursumer/cbioportal,angelicaochoa/cbioportal,pughlab/cbioportal,onursumer/cbioportal,n1zea144/cbioportal,n1zea144/cbioportal,zhx828/cbioportal,sheridancbio/cbioportal,cBioPortal/cbioportal,n1zea144/cbioportal,sheridancbio/cbioportal,cBioPortal/cbioportal,n1zea144/cbioportal,pughlab/cbioportal,d3b-center/pedcbioportal,zhx828/cbioportal,d3b-center/pedcbioportal,onursumer/cbioportal,mandawilson/cbioportal,angelicaochoa/cbioportal,onursumer/cbioportal,angelicaochoa/cbioportal,sheridancbio/cbioportal,angelicaochoa/cbioportal,d3b-center/pedcbioportal,n1zea144/cbioportal,zhx828/cbioportal,angelicaochoa/cbioportal,d3b-center/pedcbioportal,pughlab/cbioportal,sheridancbio/cbioportal,pughlab/cbioportal,d3b-center/pedcbioportal,mandawilson/cbioportal,zhx828/cbioportal,mandawilson/cbioportal,n1zea144/cbioportal,pughlab/cbioportal,pughlab/cbioportal,d3b-center/pedcbioportal,pughlab/cbioportal,cBioPortal/cbioportal,angelicaochoa/cbioportal,sheridancbio/cbioportal,cBioPortal/cbioportal,cBioPortal/cbioportal,d3b-center/pedcbioportal