Review : 6546713: Link optional in Collection exception documentation to explanation

[Mike Duigou]

Hello All;

Another collections javadoc review request. This change links the "(optional)" notes in on various Collection methods to text which explains why they are not thrown by all collections. 

I have not applied the change to java.util.concurrent package javadoc. I will leave the JSR 166 maintainers.

http://cr.openjdk.java.net/~mduigou/6546713/0/webrev/

Thanks,

Mike