Fix: Setting an empty userinfo results in commercial at-sign ("@")

This commit adds a test demonstrating the flaw and the changes to fix it. According to RFC 3986 the  commercial at-sign ("@") should only be used if the user information is present. An empty userinfo is not present.

 - Add Test 20013
 - Fixed Pear Bug #20013 / Issue #3
 - See https://pear.php.net/bugs/bug.php?id=20013 (#20013)
 - See https://github.com/pear/Net_URL2/pull/3 (#3)
Package.xml preparation.