transanims: into the code

Maybe I should start a new branch once again: the amount of updates I brought to the code gets sensible, and it doesn't feel like it'd be a good idea to commit yet. The result is that I only keep on coding when I'm *the one* of my 3 daily computers which has the modified code :(

So far:

• it should be possible to add 'pop' when importing an animation (anim%u = spr:%x) to indicate that the animation should be POPed when it's done
• GobTransition has now a GobAnim field
• CompoundGob will reload_state (actually, the animation) if a POP instruction is encountered.
  

I still have to decide how the code will install a GobAnim on GobTransitions, and how following the transition will set up the transanim on the gob.