Fix missing new-line and redundant trailing dot in WARN messages

Fix missing new-line and redundant trailing dot in WARN messages

* allchblk.c (GC_get_first_part, GC_allochblk_nth): Remove '.'
before '\n' in WARN message.
* os_dep.c (GC_read_dirty, GC_mprotect_thread, GC_dirty_init):
Likewise.
* win32_threads.c (GC_start_mark_threads_inner): Likewise.
* alloc.c (GC_collect_or_expand): Remove space before '...' in WARN
message.
* dyn_load.c (GC_register_dynlib_callback): Add '\n' at the end of WARN
message.
* os_dep.c (GC_unix_mmap_get_mem, GC_unix_mmap_get_mem): Likewise.