protect PluginLoader._extra_dirs from appending None

PluginLoader.add_directory() can receive None from, for example, 
Inventory.add_directory(self.basedir()) if host_list is a custom list.
None has no reasonable interpretation other than ignore it.

Add pacman to list of package managers in setup module

RabbitMQ Contrib

Update examples/ansible.cfg with sudo_exe

Make diagram of Directory Organization best practice match the text.

The text and playbook content assumed a directory structure that didn't
match the diagram.

module needs to be passed to local_nvra

Adding it to runner's module_path makes it override local modules.

added info of required packages to build rpms

Adding default on vars_prompt

add when_changed when_failed example to docsite

--private-key tilde handling

whitespace fix

Reported hanging of no-password sudo in some cases.  Need to explore.

This reverts commit 87f6739e.

Conflicts:

	lib/ansible/utils/__init__.py

Support sudo alternatives that offer sudo-compatible interfaces

new module: sysctl to handle sysctl entry

Pacman module

add when_{failed,changed}, and extended when_{set,unset}

add apt_key module

get_service_status() is now using self.service_control() to check status

add filter_plugins to example ansible.cfg