sagews/salvus: override matplotlib backend configuration when salvus server starts up
sagews/salvus: override matplotlib backend configuration when salvus server starts up

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