Merge lp://staging/~cjwatson/ubuntu-app-launch/libclick-manifest into lp://staging/ubuntu-app-launch/14.04

Use libclick to get package manifests, saving about 0.7 seconds from Click application startup (on mako).

This is the other half of the work started in https://code.launchpad.net/~cjwatson/upstart-app-launch/libclick-pkgdir/+merge/209909, now that click 0.4.18 has landed. It converts the remaining parts of upstart-app-launch so that it no longer needs to go through the click binary at all, and does everything click-related using libclick, thereby avoiding the need to start a Python interpreter.

I've tested this manually on mako after building on porter-armhf.c.c, and run some timings. Including previous results, the median of nine runs of "time upstart-app-launch com.ubuntu.calculator_calculator_0.1.3.224" (followed by "upstart-app-stop com.ubuntu.calculator_calculator_0.1.3.224" to clean up) behaves as follows:

  Before any libclick work: 1.772 seconds
  With libclick-pkgdir: 1.037 seconds
  With libclick-pkgdir and libclick-manifest: 0.355 seconds

The combined result of my two branches is therefore a total saving of about 1.4 seconds, or about 80% of upstart-app-launch's run-time.