modify point.  other methods, replace, tr, delete, squeeze,
  lstrip, and rstrip as well.

* string.c (rb_str_rstrip_bang): remove trailing '\0' at the end
  of string.

* string.c (rb_str_lstrip_bang): do not strip '\0' from the left.


git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@4184 b2dd03c8-39d4-4d8f-98ff-823fe69b080e