DynamicList re-visited:

 - shrink() should now correctly actually shrink
 - List::transfer(DynamicList&) invokes shrink() before transferring
   contents: otherwise the ununsed allocated space is never recovered
   until much, much later.
 - DynamicList::transfer(List&) no longer throws a FatalError when
   transferring in a smaller list. The original list contents are getting
   tossed away anyhow!