fixes #79. PdfFileReader barfs when it gets a unicode _namedDest; moving Str basestring indirection from pagerange to utils, importing into both pdf and pagerange
reliably checking if we have a basestring in our builtins for Py2 and Py3 by importing the main __builtin__ rather than relying on the locally-modifiable __builtins__ dict. fixes #79
Python3 module defining the python builtin functions is called 'builtins' plural, no __
Merge pull request #82 from egbutter/master

checking for basestring in base module __builtin__ (renamed to builtins in Py3)