Incorrect API in Abaqus IO

[yangbai90]

The APIs for "Elst" and "Nset" should be well defined in Abaqus IO. Both the "Elst" block and "Nset" block should be put into two different mesh information set.

*Elst ---> for element set information
...

which should be used for elemental type boundary conditions.

*Nset---> for node set information
...

this should be used for nodal type boundary conditions.

New Abaqus IO should distinguish these different information sets.