fix tab key sending four spaces behavior.
fix tab key sending four spaces behavior.

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