editor: when switching back to editor, refocus on the same split pane; when re-opening editor and pane is split, focus on left-most split pane
editor: when switching back to editor, refocus on the same split pane; when re-opening editor and pane is split, focus on left-most split pane

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