file.c: warn File.exists?

* file.c (rb_file_exists_p): warn deprecated name.  [Bug #9041]

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@43377 b2dd03c8-39d4-4d8f-98ff-823fe69b080e
* 2013-10-22

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@43378 b2dd03c8-39d4-4d8f-98ff-823fe69b080e