Checks that place is a declaration-env with certain properties.
If unknown-allowed is
NIL, and declaration-env
contains unknown declaration specifiers, an continuable
error is signalled. If the
CONTINUE restart is invoked,
place is set to an declaration-env with all the unknown declaration specifiers
If warn-only is true, warnings instead of errors are signalled, and
check-declaration-env behaves as if the
restart was invoked.
Signals an error of type
declaration-env is not a declaration-env.
Signals continuable errors, or warnings, under the circumstances described above.