rtt-2.0-mainline branch updated with Thread/Activity classes

I've finished unit testing the new Thread and Activity classes on
gnulinux, so I pushed them as a patch to the rtt-2.0-mainline git

They are at this stage purely add-on, so should not break existing
code (although minor changes in fosi.h and fosi_internal.h were

There will be smaller patches coming up to extend the unit tests a
little bit, and finally, make this the default activity of newly
created components. Also, none of the XML documentation has been
updated yet, but the api docs are in good shape.

We also need to think over how this will influence OCL, and in
particular the DeploymentComponent, because the Activity class casts a
shadow over the PeriodicActivity (partially) and NonPeriodicActivity
(fully) classes.