Add two missing members from the extension hash containers. The first is

the type name 'data_type', which is specified by the SGI spec as being
the correct type name for the mapped type. The second is an overload of
insert found in standard containers, taking an iterator as a 'hint'
(which we ignore in the standard containers as well). libstdc++'s
implementation includes these overloads, and they are needed to make
insert_iterator work (which I suspect is the real motivation for
including them in the standard containers).

The motivation for including these overloads of insert and leaving the
mapped_type typedef is to make it easier for clients to migrate to the
standard containers.

llvm-svn: 136538