<Core Libs Dev>[9] Review Request for 8030709: Tidy warnings cleanup for java.lang package

[alexander stepanov]

Hello,

Could you please review the fix for the following bug:
https://bugs.openjdk.java.net/browse/JDK-8030709

Webrev corresponding:
http://cr.openjdk.java.net/~yan/8030709/webrev.00/

Just a minor cleanup of javadoc to avoid tidy warnings; no other code 
affected.

BigInteger.java from java.lang was also touched.

Thanks.

Regards,
Alexander