Fix typos in comments

Fix typos in comments

* blacklst.c: Fix typo ("even though").
* cord/cordbscs.c: Fix typo ("exponentially").
* cord/cordxtra.c: Fix typo ("represented").
* dyn_load.c: Fix typos ("uncollectible", "occurred").
* extra/AmigaOS: Fix typos ("specific", "necessary", "always",
"effectiveness").
* finalize.c: Fix typo ("descendants").
* include/cord.h: Fix typo ("idiosyncrasies").
* include/gc.h: Fix typo ("collectible").
* include/gc_allocator.h: Fix typos ("allocator", "[un]collectible").
* mach_dep.c: Fix typo ("erroneously").
* malloc.c: Fix typos ("[un]collectible", "pointer-free",
"initialization").
* mallocx.c: Fix typos ("largely", "pointer-free", "uncollectible").
* mark.c: Fix typos ("[un]collectible", "even though").
* misc.c: Fix typo ("erroneously").
* os_dep.c: Fix typos ("non-addressable", "happening", "pointer-free").
* tests/test.c: Fix typos ("uncollectible", "reversed").
* tests/test_cpp.cc: Fix typos ("[un]collectible").
* typd_mlc.c: Fix typo ("copyright").
* win32_threads.c: Fix typos ("optimization", "uncollectible").