...by reverting part of 6f50961e "remove more
rtl::OUString and OString prefixes"

Change-Id: I50d37f437bb6f760c0d3990faaf71084913520f0
Reviewed-on: https://gerrit.libreoffice.org/65169
Tested-by: Jenkins
Reviewed-by: Stephan Bergmann <sbergman@redhat.com>