Added reserve() method to allow nested classes or similar related users of

Added reserve() method to allow nested classes or similar related users of
the same segment to safely bite off pieces of the same shared segment. Still
need to convert the callers.

The reserve() method is useful for single-users as well because it allows
to check that a segment has enough bytes allocated for its single user.

Changed theSize type from int to "size of any single object in RAM" size_t.