Make TracePoint.stat a singleton method again (#2726)

[Bug #16399]

test/ruby/test_settracefunc.rb

@@ -2266,4 +2266,8 @@ class TestSetTraceFunc < Test::Unit::TestCase
     bar
     EOS
   end
+
+  def test_stat_exists
+    assert_instance_of Hash, TracePoint.stat
+  end
 end

tool/test/testunit/test_parallel.rb

@@ -113,7 +113,7 @@ module TestParallel
 
         result = Marshal.load($1.chomp.unpack("m")[0])
         assert_equal(5, result[0])
-        assert_equal(12, result[1])
+        assert_equal(17, result[1])
         assert_kind_of(Array,result[2])
         assert_kind_of(Array,result[3])
         assert_kind_of(Array,result[4])

trace_point.rb

@@ -114,7 +114,7 @@ class TracePoint
   #  It may be changed in future.
   #
   #  This method is only for debugging TracePoint itself.
-  def stat
+  def self.stat
     __builtin_tracepoint_stat_s
   end