fix interaction between WrapFS._file_wrap and WrapFS.setcontents
fix interaction between WrapFS._file_wrap and WrapFS.setcontents

PyFilesystem/pyfilesystem,zopyx/pyfilesystem,Konubinix/pyfilesystem,rivenz/pyfilesystem,flying-circus/pyfilesystem,pmitros/pyfs,pombreda/pyfilesystem,pmitros/pyfs,piranna/pyfilesystem