* libguile/struct.h (SCM_VTABLE_BASE_LAYOUT): Layout is a "pr" field.
* module/ice-9/boot-9.scm (record-type-vtable): Record vtable fields are
writable.
(<parameter>): "pw" fields.
* module/oop/goops.scm (<class>, %compute-layout): <read-only> fields
are "pw" underneath.
* module/rnrs/records/procedural.scm (record-type-vtable)
(record-constructor-vtable, make-record-type-descriptor): Use "pw"
fields in vtables.
* module/srfi/srfi-35.scm (%condition-type-vtable)
(struct-layout-for-condition): "pw" fields in vtables.
* test-suite/tests/goops.test:
* test-suite/tests/structs.test: Use "pw" fields only.
* benchmark-suite/benchmarks/structs.bm: Update for make-struct/no-tail,
to use pw fields, and also to remove useless tests that the compiler
would optimize away.
* doc/ref/api-data.texi (Vtables): Add a note about the now-vestigial
permissions character and update documentation.
(Structure Basics, Meta-Vtables): Update examples.
* libguile/hash.c (scm_i_struct_hash): Remove code that would handle
opaque/self fields.
* libguile/print.h (SCM_PRINT_STATE_LAYOUT): Use "pw" fields.
* libguile/struct.c (scm_struct_init): Simplify check for hidden
fields.
* libguile/values.c (scm_init_values): Field is "pw".
