rdoc-mode.el: fill indented block

* misc/rdoc-mode.el (rdoc-fill-paragraph): fill indented block by
  list.

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@45333 b2dd03c8-39d4-4d8f-98ff-823fe69b080e
NEWS: change at r45327

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@45334 b2dd03c8-39d4-4d8f-98ff-823fe69b080e