Fetch web page with Vala and Soup

Hello,

I'm lately using the Vala language widely. I find it a great and well designed language.

You may know I'm the maintainer of Freespeak. This program is written in Python. Now I'm rewriting it in Vala, both for providing a good and really simple API in C and for learning Vala.

I will now paste a snippet from the new freespeak code that I use for creating a cancellable asyncronous operation for fetching a web page using libsoup either with a GET or a POST method.

Here's the snippet at refactory.