Addresses GB 5

The wording describes example code including the call of a move constructor, but there is no requirement stated that T be move constructible.

We would like to add a new Para 1 before existing paragraph:

Requires: Type T shall be MoveConstructible (Table 20) and MoveAssignable (Table 22).

However the MoveAssignable concept currently does not cover cases where the source and destination types may differ.