remove String#to_a

see https://github.com/rails/rails/issues/15471
Merge branch 'finn/rails4-issue-15471/remove-String-to_a' of https://github.com/marutosi/openproject into fix/remove-string-to_a
Remove String#to_a usage from SortHelper

Signed-off-by: Alex Coles <alex@alexbcoles.com>
Remove String#to_a usage from CopyModel

Signed-off-by: Alex Coles <alex@alexbcoles.com>
Merge pull request #1800 from opf/fix/remove-string-to_a