Implement/test/fix prof-related mallctl's.

Implement/test/fix the opt.prof_thread_active_init,
prof.thread_active_init, and thread.prof.active mallctl's.

Test/fix the thread.prof.name mallctl.

Refactor opt_prof_active to be read-only and move mutable state into the
prof_active variable.  Stop leaning on ctl-related locking for
protection.

test/unit/prof_reset.c

@@ -22,6 +22,8 @@ TEST_BEGIN(test_prof_reset_basic)
 	size_t sz;
 	unsigned i;
 
+	test_skip_if(!config_prof);
+
 	sz = sizeof(size_t);
 	assert_d_eq(mallctl("opt.lg_prof_sample", &lg_prof_sample_orig, &sz,
 	    NULL, 0), 0,
@@ -90,6 +92,8 @@ TEST_BEGIN(test_prof_reset_cleanup)
 	void *p;
 	prof_dump_header_t *prof_dump_header_orig;
 
+	test_skip_if(!config_prof);
+
 	active = true;
 	assert_d_eq(mallctl("prof.active", NULL, NULL, &active, sizeof(active)),
 	    0, "Unexpected mallctl failure while activating profiling");