patch : Provide better link for skip list description (CR 6495521)

[Mike Duigou]

I've posted a patch for review that updates the link to "skip list" to point to the wikipedia description rather than to Bill Pugh's home page (which makes no mention of skip lists).

http://cr.openjdk.java.net/~mduigou/6495521/webrev.0/webrev/

The link now points to <http://en.wikipedia.org/wiki/Skip_list>. The only alternative link that might be viable is <ftp://ftp.cs.umd.edu/pub/skipLists/> however I think it would be best to stick with an http link.

I've also added target="_top" so that the page is not opened within the frame but instead within the whole tab/window. This appears to be somewhat consistent with other uses of target attribute, where it is used, though there are "_blank" values used as well.

Comments and alternatives welcome. 

Mike