Validate the running PHP version against the dependency. The implicit assumption
is that the installer's PHP version is the same as the final script's PHP version.
As with all dependency validation, true is returned on success, PEAR_Error on failure
for required dependencies (and the PHP dependency is required). If the
options are specified, an array containing the error message will be returned instead.
The dependency xml as represented in parsing
throws no exceptions thrown
This function can not be called statically.