Added DEFGENERIC form for SPACING-VALUE-TO-DEVICE-UNITS.
Added DEFGENERIC form for XICALLY-CONTENT-SR**.
Added DEFGENERIC form for XICALLY-CONTENT-SR***.
Added DEFGENERIC form for BOX-LAYOUT-MIXIN/XICALLY-COMPOSE-SPACE.
Added DEFGENERIC form for BOX-LAYOUT-MIXIN/XICALLY-ALLOCATE-SPACE-AUX*.
Added DEFGENERIC form for BOX-LAYOUT-MIXIN/XICALLY-ALLOCATE-SPACE.
Removed lots of commented-out code.
Added DEFGENERIC form for TABLE-PANE-ROW-SPACE-REQUIREMENT.
Added DEFGENERIC form for TABLE-PANE-COL-SPACE-REQUIREMENT.
Removed method incorrectly-named SHEET-DISOWNED-CHILD.