* class.c: unify names of vm state version counters to 'serial'.
  This includes renaming 'vm_state_version_t' to 'rb_serial_t',
  'method_state' to 'method_serial', 'seq' to 'class_serial',
  'vmstat' to 'constant_serial', etc.

* insns.def: ditto
* internal.h: ditto
* vm.c: ditto
* vm_core.h: ditto
* vm_insnhelper.c: ditto
* vm_insnhelper.h: ditto
* vm_method.c: ditto

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@43595 b2dd03c8-39d4-4d8f-98ff-823fe69b080e