* lib/csv.rb: If skip_lines is set to a String, convert it to a Regexp
  to prevent the alternative, which is that each line in the CSV gets
  converted to a Regexp when calling skip_lines#match.



git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@43823 b2dd03c8-39d4-4d8f-98ff-823fe69b080e