Add ability to query unity for capabilities/version

[Michael Terry]

I develop deja-dup. I currently use an appindicator to convey progress and to show a few menu items during a backup. For natty, I was excited to port those over to the launcher icon support in libunity and do away with the appindicator.

However, I now understand that dynamic QLs won't be available in time for natty (bug 729074). So I may go back to appindicators for natty.

But this got me thinking. Imagine for oneiric, when QLs are fixed. And the same version of deja-dup could be run in both natty and oneiric.

Ideally there would be a way to query version or (even more ideally) capabilities. So that I could use either an appindicator or libunity depending on how capable the version of unity is.

ProblemType: Bug
DistroRelease: Ubuntu 11.04
Package: libunity3 3.6.8-0ubuntu1
ProcVersionSignature: Ubuntu 2.6.38-7.38-generic 2.6.38
Uname: Linux 2.6.38-7-generic x86_64
Architecture: amd64
Date: Fri Mar 25 15:55:57 2011
ProcEnviron:
 LANGUAGE=en_US:en
 PATH=(custom, user)
 LANG=en_GB.utf8
 LC_MESSAGES=en_US.utf8
 SHELL=/bin/bash
SourcePackage: libunity
UpgradeStatus: Upgraded to natty on 2010-09-28 (178 days ago)