pad string. [ruby-talk:70482]

* string.c (rb_str_rjust): ditto.

* string.c (rb_str_center): ditto.

* string.c (rb_str_justify): utility function.

* eval.c (rb_add_method): call singleton_method_added or
  method_added for every method definition (after ruby_running).
  [ruby-talk:70471]

* array.c (rb_ary_reverse_bang): Array#reverse! should not return
  nil even for arrays sized less than 2.

* io.c (argf_eof): should not block after reading all argument
  files. (ruby-bugs-ja PR#449)


git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@3742 b2dd03c8-39d4-4d8f-98ff-823fe69b080e