Update issue #136 : Close application when last remaining document window closed, not when first-opened document window closed.
(fixes bug in MFC multiple top-level window new project wizard).
Reassign m_pMainWnd to first remaining document window when first document window closed.

git-svn-id: http://graph-studio-next.googlecode.com/svn/trunk@222 c2f33eb2-41b2-391d-4cb4-d9d0608729ba