add a history buffer.
add a history buffer.

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