erb: cast string to array for ruby 1.9

In ruby 1.9.x (not in use yet), the strings no more have a map()
methods:

undefined method `map' for "#wikimedia-operations":String
(NoMethodError)

To ensure future compatibility with ruby1.9, we simply cast the list of
channels as an array to make sure the result will always have the map()
method.

With ruby 1.8:

  >> "my string".map{ |string| string }
  => ["my string"]

With ruby 1.9 that fails:

  >> "my string".map{ |string| string }
  => #<NoMethodError: undefined method `map' for "my string":String>

But casting to an array will make it work:

  >> Array( "my string" ).map { |string| string }
  => ["my string"]
  >>

Change-Id: I50d37166e17b84018a011a1e64a488cce183feed
Merge "erb: cast string to array for ruby 1.9" into production