Fix 'fileFromPath not defined or not exported'  error
which occurs with perl 5.18.   the @ISA=qw(PGcore) statement should never have been there, but it does not seem to be causing the problem.  The workaround/fix for the moment is to fully qualify the function name as WeBWorK::PG::IO::fileFromPath.
Merge pull request #144 from mgage/master_IO_fix

Fix 'fileFromPath not defined or not exported'  error