Split the threads support

Now we use the --disable-multi-core to enable or not
multi core rendering. The thread support is chcked in
order to have multi core.
Update the files using the multi core.
Also start adding configure checks to support wgl
Add the WGL backend

It is not fully working, given that gl support on
a virtualbox machine is not complete but is good for testing
Be sure to initialize the extensions too
Check for the needed extension