advpack: Implement LaunchINFSection on top of DoInfInstall

[Markus Amsler]

James, I just saw your advpack patches.
Only patch 4 (* Add stubs for the file save/restore functions), 
Makefile.in gets a merge conflict with mine first 1 (Move inf install 
functions to install.c ). The rest applies fine (some offset warnings), 
and builds without warning. Should I rediff against yours or you against 
mine? Is there a better way to coordinate our efforts?
My LaunchINFSectionEx patch seems to improve bug 3636.

Markus