Replace some std::maps/sets with map/set container typedefs.
ie. Switchable between btree and std.
Limit this change to sets/maps keyed by tweet/user ID, and
(for maps) which have a trivially movable value type.
Do not rely on container move semantics to clear source CIDS sets.
Add btree move assignment operators and move constructors.
Minor fix to PCH dependency generation in makefile.
Remove redundant declaration.
Implement a revision counter for userdata objects.