Allow adding of blocks to a subproject task in the super project

[michaeljbishop]

As long as the super-project can reference tasks created in the sub-project, allow those tasks to have execution blocks attached to them in the super-project Rakefile.

So, to be clear, here's a task in in the subproject, located at foo.

task :hello do
  p "HELLO"
end

And here is the super-project:

subproject 'foo'

task 'foo:hello' do
  p "WORLD"
end

Now, when executing the super project:

$ rake foo:hello
HELLO
WORLD

The sub-project blocks are all executed before the super-project blocks.