install special raw Lisp behavior

Please first see return-last for relevant background.

This table is for advanced users only, and requires an active trust tag (see defttag). We recommend that you do not modify this table directly, but instead use the macro defmacro-last. Here we augment that discussion with some highly technical observations that can probably be ignored if you use defmacro-last.

This table has a :guard requiring that each key be a symbol defined in raw Lisp, generally as a macro, and requiring that each non-nil value be associated either with a symbol that names a macro defined in ACL2, or else with a list of one element containing such a symbol. The table can only be modified when there is an active trust tag; see defttag. If a key is associated with the value nil, then that key is treated as though it were not in the table.

Note that keys of this table are not eligible to be bound by flet. The current value of this table may be obtained by evaluating the form (table-alist 'return-last-table (w state)). The built-in constant *initial-return-last-table* holds the initial value of this table.