$required = true
This validates against actual in-memory extensions, and will not attempt to locate extensions on disk. To do this, a dependency should be a package dependency with the <providesextension> tag.
As with all dependency validation, true is returned on success, PEAR_Error on failure
for required dependencies. If the
ignore-errors options are specified, an array containing the
error message will be returned instead.
dependency contents as parsed from xml
Whether this is a required or optional dependency
throws no exceptions thrown
This function can not be called statically.