[Ming-dev] garbage collector updates

[strk <st...@ke...>]

I've updated the garbage collector to not rely on 
blocks list to be unmodified. This is because sometime
an object destructor will destroy other objects
(see destroySWFJpegBitmap_andInput) so we need not
to use cached pointers to node that are already 
destroied by other destructors.

The new code keeps destroying the firstnode until
it evaluates to false (is NULL). Each node destructor
will remove that node from the list and modify the
firstnode pointer.

--strk;