* module/system/base/ck.scm: New module.
* module/srfi/srfi-9.scm: Import (system base ck).
(getter-type, getter-index, getter-copier): Convert incoming argument
convention to CK form.
(define-tagged-inlinable): Convert return value convention for key
lookup to CK form.
* module/srfi/srfi-9/gnu.scm: Import (system base ck).
Rename '%set-fields-unknown-getter' to 'unknown-getter'.
(c-list, c-same-type-check): New macros.
(%set-fields): Using the CK abstract machine, arrange to check (at
macro expansion time) that all of the getters in head position
correspond to the same record type.
* test-suite/tests/srfi-9.test: Add test.
