Macros with rest arguments can now be translated (again)

Macros with rest arguments can now be translated (again)

Attempting to translate any macro with a rest arg always caused an
error during translation because bogus Maclisp-style lexpr lambda
expressions were being constructed.  This used to work under Maclisp,
of course, but this has failed for decades under CL.

Now we use CL-style rest args instead of Maclisp-style lexprs when
defining functions and macros with DEFMTRFUN.

No problems with the test suite or share test suite.
tests/rtest_translator.mac runs as expected, with new tests.