Persist glob when replacing a path

When Rails::Paths::Root's []= is used to replace a path it should persist the previous path's glob. Without passing the glob along we get gnarly bugs when trying to wire up things like engines.

    module FooEngine
      class Engine < ::Rails::Engine
        isolate_namespace FooEngine

        config.paths['config/initializers'] = "lib/foo_engine/initializers"
      end
    end

    ## Example of behaviour before this commit.
    #
    # Before the initializer override:
    >> FooEngine::Engine.config.paths["config/initializers"].glob
    => "**/*.rb"

    # After the initializer override:
    >> FooEngine::Engine.config.paths["config/initializers"].glob
    => nil

    ## Example of behaviour after this commit.
    #
    # Before the initializer override:
    >> FooEngine::Engine.config.paths["config/initializers"].glob
    => "**/*.rb"

    # After the initializer override:
    >> FooEngine::Engine.config.paths["config/initializers"].glob
    => "**/*.rb"

1 files changed, 2 insertions, 1 deletions

diff --git a/railties/lib/rails/paths.rb b/railties/lib/rails/paths.rb
index 6cd9c7bc95..316ecca87b 100644
--- a/railties/lib/rails/paths.rb
+++ b/railties/lib/rails/paths.rb
@@ -51,7 +51,8 @@ module Rails
       end
 
       def []=(path, value)
-        add(path, :with => value)
+        glob = self[path] ? self[path].glob : nil
+        add(path, :with => value, :glob => glob)
       end
 
       def add(path, options={})