PPM: test before download

The PPM has a problem when a package with lots of dependencies is to be installed, and one or more is/are not in the repository or fails to download for some other reason.

There is the problem of some packages in the 'update' repositories (Ubuntu and Debian) changing, so the local package database is out-of-date, so the package is not in the repository.

To fix this, the PPM now checks that all packages to be downloaded are available online before starting to download and install any of them. If one or more packages is/are missing, the entire operation is aborted -- and the user is advised to update the local package database.

Woof commit:
http://bkhome.org/fossil/woof2.cgi/info/7775c0b271

Tags: woof