mem-leak in PD_Document

[Mike Nordell]

It seems to me the destructor of PD_Document should clean up the contents of
its member m_vecLists, but since object ownership is sometimes a bit "fuzzy"
(e.g. classes don't keep their private parts to themselves, sometimes
letting their children play with them) I'm not 100% sure. Anyone?

To reproduce the leak, just create a list and exit AbiWord.

/Mike