While-loop/refactoring.
While-loop/refactoring.

-While-loop:
	- rewrite to any smaller term (rather than skip only).
	- try rewriting pairs in par([..]) before rewriting single expression.
-Refactoring: removed rewrite of single expressions in par as it's
subsumed by pair-wise rewrite.

abakst/symmetry,abakst/symmetry,abakst/symmetry,abakst/symmetry