webapp/sagews: fix misc.get_extension is not a function -- #3564
webapp/sagews: fix misc.get_extension is not a function -- #3564

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