Ruby

• vm_trace.c: rename and add TracePoint APIs.
  (1) TracePoint.new(...){...} creates a new trace point
  but does not make it enable.
  (2) TracePoint.trace(...){...} creats a new trace point
  and enable it (same as old behavior).
  (3) TracePoint#enable make it enable (renamed from TracePoint#retrace).
  If block given, when enable only in block.
  (4) TracePoint#disable make it disable (renamed from TracePoint#untrace).
  If block given, when disable only in block.
  (5) TracePoint#enabled? returns this trace is enable or not.
• test/ruby/test_settracefunc.rb: addd tests.

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@37753 b2dd03c8-39d4-4d8f-98ff-823fe69b080e