RFR: 8154482: javadoc tool must support legacy doclet and taglet

[Kumar Srinivasan]

Hello,

Please review  fix for:
https://bugs.openjdk.java.net/browse/JDK-8154482

Webrev at:
http://cr.openjdk.java.net/~ksrini/8154482/webrev.00/

Thanks
Kumar