Ruby

merges r21536 from trunk into ruby_1_9_1.

• vm.c (rb_vm_inc_const_missing_count, ruby_vm_const_missing_count):
  added.
• vm_insnhelper.h: ditto.
• variable.c (rb_const_get_0), insns.def: Constants should not be
  cached if const_missing is called. [ruby-core:21059] [Bug #967]
• bootstraptest/test_class.rb: add a test.

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/branches/ruby_1_9_1@21574 b2dd03c8-39d4-4d8f-98ff-823fe69b080e