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.

test/include/test/test.h

@@ -187,12 +187,22 @@ f(void)									\
 	p_test_init(#f);
 
 #define	TEST_END							\
+	goto label_test_end;						\
+label_test_end:								\
 	p_test_fini();							\
 }
 
 #define	test(tests...)							\
 	p_test(tests, NULL)
 
+#define	test_skip_if(e) do {						\
+	if (e) {							\
+		test_skip("%s:%s:%d: Test skipped: (%s)",		\
+		    __func__, __FILE__, __LINE__, #e);			\
+		goto label_test_end;					\
+	}								\
+} while (0)
+
 void	test_skip(const char *format, ...) JEMALLOC_ATTR(format(printf, 1, 2));
 void	test_fail(const char *format, ...) JEMALLOC_ATTR(format(printf, 1, 2));