GENER series of history plot may not work with TOUGHMP result

[Angus Yeh]

The code assumes all t2listing objects having generation table, which is bad. TOUGHMP does not have that in t2listing, using GOFT is required.

[Angus Yeh]

Fix Issue #30 by checking if generation table exist in t2listing.

→ <<cset a3e3b39329b1>>