Duplicate possible frozen string from route

Ruby 1.9 freezes Hash string keys by default so where a route is
defined like this:

get 'search' => 'search'

then the Mapper will derive the action from the key. This blows up
later when the action is added to the parameters hash and the
encoding is forced.

Closes #3429
Merge branch '3-2-stable' into collection_sum_fix