Added rewrites for EXPT and SQRT which are `enabled' by using EXPT and

Added rewrites for EXPT and SQRT which are `enabled' by using EXPT and
SQRT like this:

	((access SQRT system-global-environment) 6.7)

i.e. they dispatch of (CALL %invoke-remote-operator ...)  (declare
(usual-integrations)) should be changed to make operator references to
these standard procedures into global references.

SQRT just does constant folding.  EXPT also expands to a small
expression trees of <= some number of generic multiplies for a small
exact integer exponent.