RFR: 8182611: @extLink taglet ignores text after first newline.

[Jonathan Gibbons]

Please review a simple fix to the regex used to analyze the content of 
an {@extLink } tag.

The fix is to use DOTALL mode for the regex, and for good measure, to 
ensure the match is up to the end of the line.

JBS: https://bugs.openjdk.java.net/browse/JDK-8182611

The one-line fix is in the comments for the JBS issue:
https://bugs.openjdk.java.net/browse/JDK-8182611?focusedCommentId=14094548&page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel#comment-14094548

-- Jon