Fix identification of installed packages in Ubuntu 14.04

Ubuntu 14.04 comes with an apt-get that produces slightly differently
formatted output, which makes our code for detecting installed packages
fail.  This adjusted code works with Ubuntu 14.04 as well as older
Ubuntu and Debian versions.

installation/prereqs.py

@@ -69,7 +69,6 @@ def install_packages(arguments, *packages):
             default=True)
         if not aptget_approved: aptget = False
     if aptget:
-        installed_anything = False
         aptget_env = os.environ.copy()
         if arguments.headless:
             aptget_env["DEBIAN_FRONTEND"] = "noninteractive"
@@ -81,13 +80,16 @@ def install_packages(arguments, *packages):
         aptget_output = subprocess.check_output(
             [aptget, "-qq", "-y", "install"] + list(packages),
             env=aptget_env)
+        installed = {}
         for line in aptget_output.splitlines():
-            match = re.search(r"([^ ]+) \(.* \.\.\./([^)]+\.deb)\) \.\.\.", line)
+            match = re.match(r"^Setting up ([^ ]+) \(([^)]+)\) \.\.\.", line)
             if match:
-                need_blankline = True
-                installed_anything = True
-                print "Installed: %s (%s)" % (match.group(1), match.group(2))
-        return installed_anything
+                package_name, version = match.groups()
+                if package_name in packages:
+                    need_blankline = True
+                    installed[package_name] = version
+                    print "Installed: %s (%s)" % (package_name, version)
+        return installed
     else:
         return False