document debug modes a little more
document debug modes a little more

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