update-manager: improve trisquel version detection

Closes #12545

helpers/DATA/update-manager/trisquel-versions.patch

@@ -0,0 +1,27 @@
+--- UpdateManager/Core/utils.py	2015-10-21 04:05:26.461825091 +0200
++++ UpdateManager/Core/utils.py.new	2015-10-21 04:03:30.461825105 +0200
+@@ -426,7 +426,7 @@
+     # From spec, first if ubuntu-desktop is installed, use that.
+     # Second, grab first installed one from DistUpgrade.cfg.
+     # Lastly, fallback to ubuntu-desktop again.
+-    meta_pkgs = ['ubuntu-desktop']
++    meta_pkgs = ['trisquel','trisquel-mini','trisquel-sugar']
+ 
+     try:
+         meta_pkgs.extend(sorted(_load_meta_pkg_list()))
+@@ -439,13 +439,13 @@
+         cache_pkg = cache[meta_pkg] if meta_pkg in cache else None
+         if cache_pkg and cache_pkg.is_installed:
+             return meta_pkg
+-    return 'ubuntu-desktop'
++    return 'trisquel'
+ 
+ 
+ def get_ubuntu_flavor_name(cache=None):
+     """ try to guess the flavor name based on the running desktop """
+     pkg = get_ubuntu_flavor_package(cache=cache)
+-    lookup = {'ubuntustudio-desktop': 'Trisquel Studio'}
++    lookup = {'trisquel-mini': 'Trisquel Mini', 'trisquel-sugar': 'Trisquel Sugar' }
+     if pkg in lookup:
+         return lookup[pkg]
+     elif pkg.endswith('-desktop'):