Add SIDE-EFFECT-FREE-AST-MIXIN as a superclass for some ASTs.
Add SIDE-EFFECT-FREE-AST-MIXIN as a superclass for some ASTs.

vtomole/SICL,vtomole/SICL,vtomole/SICL,clasp-developers/SICL,clasp-developers/SICL,clasp-developers/SICL,clasp-developers/SICL,vtomole/SICL