Revert "reverted back to file-only checks, changed to file_exists()"

This reverts commit d234b8e2128356a5d7c76e7d7048c21a26bd49c2.
final workaround for PHP bug 52065
Merge pull request #48 from rindeal/feature/config-fixes

fix for PHP warning "is_file(): open_basedir restriction in effect", round 2