lastline and lastmatch in the thread struct for later restore.

* eval.c (rb_thread_save_context): restore lastline and lastmatch.

* numeric.c (flo_to_s): should handle negative float value.

* class.c (rb_include_module): should check whole ancestors to
  avoid duplicate module inclusion.

* string.c (trnext): should check backslash before updating "now"
  position.


git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@1746 b2dd03c8-39d4-4d8f-98ff-823fe69b080e