DERBY-6552 The public api includes methods inherited from superclasses which aren't in the public api and so have no javadoc comments

Patch derby-6552-firewall-balm:

- Use an explicit <get> task to download the required package lists
  for the external Java SE and J2EE Javadocs we want to link to from
  our published API docs.

- Remove the explicit boot classpath set to 16 level lest we get
  errors generating the docs for classes which require a higher
  level. The new method needs to see all source file to be able to
  resolve links and inherit javadocs. The first time the publishedapi
  target is built, the package lists will be downloaded and cached in
  local directories. Added svn ignore setting for those. On subsequent
  builds, the cached values will be used. If behind a firewall the
  first time one builds, one needs to let ant know how to bypass the
  firewall, e.g. this way in bash:

     > export ANT_OPTS="-Dhttp.proxyHost=proxyserver -Dhttp.proxyPort=80"

  in bash(1).



git-svn-id: https://svn.apache.org/repos/asf/db/derby/code/trunk@1603943 13f79535-47bb-0310-9956-ffa450edef68