Package resources should support pessimistic versioning

The package resource should let you ensure a range of versions, similiar to how pessimistic versioning works with gems.

This would let you ensure a range, and have it act like `ensure => latest` but only install minor or patch level upgrades depending on how you specify the version.

This would create less work for admins, as they could get bugfix releases automatically, but not have to worry about a breaking major change version getting in without them explicitly choosing it.