Allow raid_su and raid_sw to be blank, even if it is not recommended.

There could be some cases when you want to omit these choices.

Bug reported by Gilles Dubreuil.
Make Exec['again'] optional. As a result puppet-common is optional.

Although if you remove all the features, it's not as awesome anymore :)
Support LVM thin provisioning.

This adds the ability to do LVM thin provisioning. If you haven't fully
read 'man 7 lvmthin' then please do as this will answer most of your
questions. LVM thin provisioning is used for doing one form of GlusterFS
snapshots.
Include glusterfs-api package for client and server.

In the future this package should only be pulled in when a known
dependency tells puppet-gluster that it needs it. For now it's fine.
In any case, this is Mostly Harmless (tm).