* libguile/threads.c (fat_mutex_lock): allow-external-unlock mutexes
can't be recursive, but a recursive lock attempt can be unblocked by
an external thread, so these mutexes shouldn't throw an error on
recursive lock attempts.
* test-suite/tests/srfi-18.test: Add tests.
* module/srfi/srfi-18.scm (<mutex>): Define as a wrapper type around
Guile mutexes.
(thread-mutexes): New variable.
(with-thread-mutex-cleanup): New facility to abandon mutexes on
SRFI-18 thread exit. Not yet used.
(make-thread): Use SRFI-18 interfaces.
(make-mutex): Reimplement for our boxed mutexes.
(mutex-state): Adapt.
(mutex-lock!): Adapt.
(mutex-unlock!): Adapt.
* test-suite/tests/srfi-18.test: Don't assume that SRFI-18 mutexes are
the same as Guile mutexes.
* module/srfi/srfi-18.scm: Use srfi-35 conditions instead of our
home-grown equivalent system.
(thread-exception-handlers): Remove unused table.
(srfi-18-exception-handler): Always capture key consed to args; no
special case for bare key.
* test-suite/tests/srfi-18.test (provided?): Adapt to reason always
being key+args.
* test-suite/tests/srfi-18.test: Enclose the tests in a begin instead of
an and. Before, they were not being run, for some reason I don't
fully understand.
* module/language/tree-il/compile-glil.scm (flatten): For applications in
"drop" context, allow the procedure to return unspecified values
(including 0 values).
* test-suite/tests/tree-il.test ("application"): Adapt test.
* module/srfi/srfi-18.scm (wrap): Clarify.
* test-suite/tests/srfi-18.test: Fix so that the expression importing
srfi-18 is expanded before the tests. However the tests are still
failing, something about 0-valued returns...
