sagews: improve error message -- issue #2245
sagews: improve error message -- issue #2245

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