file.c: join with /
git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@57960 b2dd03c8-39d4-4d8f-98ff-823fe69b080e
file.c: join with /
and fix the document. [ruby-core:79579] [Bug #13223]
git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@57960 b2dd03c8-39d4-4d8f-98ff-823fe69b080e