* module/rnrs/6/exceptions.scm: Remove dependency on (rnrs syntax-case);
rewrite guard and guard0 in using syntax-rules in terms of syntax-case.
* module/rnrs/6/syntax-case.scm: Add syntax-violation implementation.
* module/rnrs/6/exceptions.scm: (guard0, guard): New syntax.
* module/rnrs/records/6/procedural.scm: (r6rs-raise-continuable): Can't
use `raise' here because it's exported by (rnrs exceptions); use plain
old `throw' instead.
* test-suite/Makefile.am: Add tests/r6rs-exceptions.test to SCM_TESTS.
* test-suite/tests/r6rs-exceptions.test: New file.
along with its dependencies.
* module/Makefile.am: Add new R6RS libraries below to RNRS_SOURCES.
* module/rnrs/6/conditions.scm, exceptions.scm, syntax-case.scm: New files.
* module/rnrs/io/6/simple.scm: New file.
* module/rnrs/records/6/procedural.scm, syntactic.scm: New files.
* test-suite/Makefile.am: Add tests/r6rs-records-procedural.test to SCM_TESTS.
* test-suite/tests/r6rs-records-procedural.test: New file.