Fixed serious bug in BatchReadOwnedPtrs where in a chain of calls to

deserialize objects if BatchReadOwnedPtrs was called more than once in the
same call chain then the second call would overwrite the SerializedPtrIDs
being used by the first call. Solved this problem by making the vector that
holds the pointer IDs local to a function call. Now BatchReadOwnedPtrs is
reentrant.

llvm-svn: 44152