--force needed to generate Manifest without distfiles

[orlitzky]

This is a mild annoyance I've had for a while. In my overlays, I have a lot packages without distfiles. (Hundreds of acct-user packages, among others). Whenever I create a new package, the process goes something like this:

$ emacs www-dot-example-dot-com-0.ebuild
$ pkgdev manifest
$ git add .
$ pkgdev commit
$ git push

and then I update the overlay on our servers, and try to install the new user. Inevitably this produces,

- acct-user/www-dot-example-dot-com-0::overlay (masked by: corruption)

because pkgdev quietly did nothing when I asked it to create the manifest. If I go back and use -f, it's fine...

$ pkgdev manifest -f
 * generating manifest: acct-user/www-dot-example-dot-com::overlay