Calling map on string now fails, rather than yielding the string.

In Ruby 1.8 "foo".map would yield "foo" once, while in Ruby 1.9 it is not
defined as a method.

Various parts of our testing code stub other methods and return strings where
arrays of strings are appropriate; this historically worked because of that
1.8 shim, and no longer does.

The same is true of String#each, which fails in the same way.

Signed-off-by: Daniel Pittman <daniel@puppetlabs.com>