Log Message:
Updated mdds1.2 to 1.2.1.

mdds 1.2.1

* multi_type_vector

  * added size() method to the element block type, which returns the
    actual size of the element block, instead of the cached size value
    stored in the parent structure that stores the element block.

  * fixed a double-deletion bug in the swap() method which would
    triggered when used with a managed element block.

* mtv::collection

  * fixed collection iterator's get() method to properly return values
    from the boolean element block.