Patch to prevent modification of the array passed in to polymorphic_path

[Thomas Lee]

Hi all,

Can I get a review or two regarding this patch? Fixes some nasty
unexpected behaviour in polymorphic_path whereby the array fed to the
method is actually modified in-place, potentially causing confusion for
client code. See the ticket for more details.

http://dev.rubyonrails.org/ticket/11363

Cheers,
T