Change special treatment of evaluate-in-inferior-repl and run-light

Change special treatment of evaluate-in-inferior-repl and run-light
editor variables.  These variables are now given buffer-local values
to disable the use of an inferior repl when either scheme-environment
or scheme-syntax-table is given a local binding that overrides the
default.  Also, these automatic bindings are only performed if the
variables do not already have buffer-local bindings.