Validate a subpackage-style dependency. This is identical to a package dependency
from a validation perspective, and so documentation for
validatePackageDependency() should be referenced for details.
Parameter
array
$dep
dependency array as defined by package.xml 2.0
boolean
$required
whether this is a required or optional dependency
array
$params
array of PEAR_Downloader_Package objects representing packages to be
downloaded that can be used to validate dependencies
