[nfs] - complete fix started in dd4dd2e91bc083a23fe7b46ae4c291c6672d32e0

Trac issue #14727 was not completely solved by the previous commit due to
exportPath's having trailing slash's, but path's not always having them.

This should restore media library sync behaviour for NFS libraries as before
fe97d68f87d6985b2bf57d8e942b36b5e7373066.