fix #5 - Breaks when a Package title != name

[giuliano108]

Fixes #5 .

When computing the set of managed packages, we can't just look them up by title in the Catalog. Because title and name can be different, we need to look into the "resource aliases" table too.

package {'arbitrarytitle': name => 'pkgname'}

I couldn't find a public API to access @aliases, hence the instance_variable_get hack... :(

The @aliases data structure looks as follows:

[4] pry(#<Puppet::Type::Aptly_purge>)> catalog.instance_variable_get :@aliases
=> {"Class[Main]"=>[["Class", "main"]],
 "Package[ubuntu-minimal]"=>[["Package", "ubuntu-minimal", :held_apt]],
 "Package[puppetlabs-release-pc1]"=>[["Package", "puppetlabs-release-pc1", :held_apt]],
 "Package[puppet-agent]"=>[["Package", "puppet-agent", :held_apt]],
 "Package[openssh-server]"=>[["Package", "openssh-server", :held_apt]],
 "Package[fortunespkg]"=>[["Package", "fortunes", :held_apt]],
 "Aptly_purge[packages]"=>[["Aptly_purge", :packages]]}