Improvements to Debian packaging targeting unstable

[andrewpollock]

This is the better version of #1906 for #662

@nicolasnoble please advise if you want me to continue directly assigning these to you, or if I should submit them unassigned.

[googlebot]

We found a Contributor License Agreement for you (the sender of this pull request) and all commit authors, but as best as we can tell these commits were authored by someone else. If that's the case, please add them to this pull request and have them confirm that they're okay with these commits being contributed to Google. If we're mistaken and you did author these commits, just reply here to confirm.

[andrewpollock]

If that's the case, please add them to this pull request and have them confirm that they're okay with these commits being contributed to Google.

@gcsideal I think you have to chime in here to make the @googlebot happy with life.

[gcsideal]

@googlebot : I know that Google would like to merge my collaboration from the Git tree of Andrew Pollock to the official gRPC Git tree. I do understand what does it mean and I accept it. I won't sue Google because of this, quite the contrary, I hope my commits will help Google and the community around gRPC to achieve whatever they want until they uphold the current license terms (which is BSD 3-Clause at the time of writing). If needed I can clearsign these words with my GnuPG key which is signed by at least one (current) Google employee.