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.
dependency array as defined by package.xml 2.0
whether this is a required or optional dependency
array of PEAR_Downloader_Package objects representing packages to be downloaded that can be used to validate dependencies
throws no exceptions thrown
This function can not be called statically.