package: pacman provider: Add purgeable feature

This small patch adds an option to the pacman provider to purge config
files.

From the manpage:

```console
$ pacman -R -h | head -n6
usage:  pacman {-R --remove} [options] <package(s)>
options:
  -b, --dbpath <path>  set an alternate database location
  -c, --cascade        remove packages and all packages that depend on them
  -d, --nodeps         skip dependency version checks (-dd to skip all checks)
  -n, --nosave         remove configuration files
```

Author: bastelfreak

Diff for: lib/puppet/provider/package/pacman.rb

@@ -25,6 +25,7 @@ def self.yaourt?
   has_feature :uninstall_options
   has_feature :upgradeable
   has_feature :virtual_packages
+  has_feature :purgeable
 
   # Checks if a given name is a group
   def self.group?(name)
@@ -191,6 +192,16 @@ def self.to_resource_hash(name, version)
 
   # Removes a package from the system.
   def uninstall
+    remove_package(false)
+  end
+
+  def purge
+    remove_package(true)
+  end
+
+  private
+
+  def remove_package(purge_configs = false)
     resource_name = @resource[:name]
 
     is_group = self.class.group?(resource_name)
@@ -201,6 +212,7 @@ def uninstall
     cmd += uninstall_options if @resource[:uninstall_options]
     cmd << "-R"
     cmd << '-s' if is_group
+    cmd << '--nosave' if purge_configs
     cmd << resource_name
 
     if self.class.yaourt?
@@ -210,8 +222,6 @@ def uninstall
     end
   end
 
-  private
-
   def install_options
     join_options(@resource[:install_options])
   end