Cleanup #165: Annihilate CkMigratableList and temporarily typedef to std::map
Much of our pre-stable-stl code grew its own mutant data structures
which could do all weird and fantastic things. CkMigratableList seems
one such. Its permits indexed random access from an array which can
have empty slots while iteration is O(containersize) instead of O(numElements).
I think much of this effort is in order to keep CkLocRec_local::localIdx
in sync with the element's actual location in the array manager's element
Nuke this structure and temporarily replace with std::map. Eventually,
even that should give way for more efficient element lookups.