vl: deftranssum hint improvement and exprsize proof that all 0-width expressions are unsigned
merge

Resolved Conflicts:
	books/centaur/vl/mlib/scopestack.lisp
	books/centaur/vl/parsetree.lisp
Various VL fixes and additions to .gitignore, just-expand
VL: move selfsize and typedecide functions out of xf-expr-size.lisp and into new files, shuffle some other stuff around
Merge

Conflicts:
	books/centaur/vl/mlib/scopestack.lisp
	books/centaur/vl/parsetree.lisp
Merge