Update PythonEval.cc -- boost::filesystem3 changed to boost::filesystem

This was necessary to make it compatible with Boost 1.53.0. The file still remains backward-compatible on earlier versions up to version 1.46.0.
Update PythonEval.h -- boost::filesystem3 changed to boost::filesystem

This was necessary to make it compatible with Boost 1.53.0. The file still remains backward-compatible on earlier versions up to version 1.46.0.
Merge pull request #212 from 5aurabhpathak/master

Updated these files to support newer versions of Boost libraries

Merging despite reported errors; the errors were reported for a version of opencog that does not have this patch in it, therefore, this patch cannot be causing them.