Add quarantine unit tests.

Verify that freed regions are quarantined, and that redzone corruption
is detected.

Introduce a testing idiom for intercepting/replacing internal functions.
In this case the replaced function is ordinarily a static function, but
the idiom should work similarly for library-private functions.

include/jemalloc/internal/private_symbols.txt

@@ -50,8 +50,10 @@ arena_prof_ctx_set
 arena_prof_promoted
 arena_ptr_small_binind_get
 arena_purge_all
+arena_quarantine_junk_small
 arena_ralloc
 arena_ralloc_no_move
+arena_redzone_corruption
 arena_run_regind
 arena_salloc
 arena_stats_merge