Factorize some of the IF and WHILE code
Factorize some of the IF and WHILE code

There was some common code for handling conditional expressions
in the implementation of IF and WHILE.  This code has now been
factorized.

Signed-off-by: Mark Ryan <88ffc4093c40652fbbf052f026a8b6147509f0aa@gmail.com>

markdryan/subtilis,markdryan/subtilis