Increase robustness when adding "malformed" packages.

[bracki]

According to https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=666726 packages may contain empty control fields, e.g. here https://github.com/nicolasff/phpredis/blob/master/debian.control.
This causes apt to fail miserably.
Wouldn't it be nice if freight stripped these fields?

Cheers,
Jan

[bracki]

Even better solution would be to use dpkg-scanpackages. Any reason why this isn't being used?