history viewer: set editor using a more sensible approach.
history viewer: set editor using a more sensible approach.

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