fix https://github.com/sagemathinc/smc/issues/1898 (hopefully) -- safari in private browsing: show_local_storage_warning broken
fix https://github.com/sagemathinc/smc/issues/1898 (hopefully) -- safari in private browsing: show_local_storage_warning broken

sagemathinc/smc,DrXyzzy/smc,tscholl2/smc,sagemathinc/smc,tscholl2/smc,tscholl2/smc,sagemathinc/smc,DrXyzzy/smc,DrXyzzy/smc,DrXyzzy/smc,tscholl2/smc,sagemathinc/smc,tscholl2/smc