Review comment 5 from schultz
Validate stored credential

git-svn-id: https://svn.apache.org/repos/asf/tomcat/trunk@1627607 13f79535-47bb-0310-9956-ffa450edef68
Review comment 6 from schultz
Create correctly sixed StringBuidler for result

git-svn-id: https://svn.apache.org/repos/asf/tomcat/trunk@1627608 13f79535-47bb-0310-9956-ffa450edef68
Review comment 8 from schultz
Allow the use of custom CredentialHandlers when creating credential
strings for storage

git-svn-id: https://svn.apache.org/repos/asf/tomcat/trunk@1627609 13f79535-47bb-0310-9956-ffa450edef68