src/LocalPath.cpp: Changed XCSoarData folder destination for iOS devices

If target is an iOS device, use the already existing "Documents" folder inside the application's sandbox instead of an XCSoarData folder.
This folder could also be accessed via iTunes, if UIFileSharingEnabled is set to YES in Info.plist.
test/test_debug: include cleanup
Trace: use class boost::intrusive::list instead of ListHead
Trace: rename "List" to "DeltaList"

.. and move to the parent class.
Trace: make the DeltaRankOp "const"
Trace: fix off-by-one bug in EraseDelta()'s initial size check

Can't erase anything if both points are edges.
Trace: use class boost::intrusive::multiset

Eliminates a good amount of unnecessary code and some runtime
overhead.
Thread: use class boost::intrusive::list instead of ListHead
Util/ListHead: remove obsolete library