Improve GC output atomicity in GC_print_obj, GC_print_all_errors

Improve GC output atomicity in GC_print_obj, GC_print_all_errors
(as well as in GC_print_backtrace, GC_print_all_smashed_proc)

* blacklst.c (GC_default_print_heap_obj_proc): Refine printed message;
output object kind; output trailing "\n".
* reclaim.c (GC_print_all_errors): Do not print object kind (before
GC_print_heap_obj call).
* dbg_mlc.c (GC_print_backtrace): Remove redundant printed "\n" after
GC_print_heap_obj call.
* reclaim.c (GC_print_all_errors): Likewise.
* dbg_mlc.c (GC_print_type): Remove (move code to GC_print_obj
replacing "p" local variable with "q").
* dbg_mlc.c (GC_print_obj): Merge adjacent GC_err_printf and
GC_err_puts invocation into a single GC_err_printf one (for output
atomicity).
* dbg_mlc.c (GC_print_all_smashed_proc): Print number of found objects
first.
* reclaim.c (GC_print_all_errors): Likewise.
* dbg_mlc.c (GC_print_all_smashed_proc): Remove printed "\n" at list
end.
* include/private/gc_priv.h (GC_print_heap_obj, GC_printf): Refine
comments.