Use Java syntax for Exception

There is a known issue when a grails app compiled on JDK6 runs on JDK7 and tries
to construct an exception written in Groovy.
http://blog.proxerd.pl/article/how-to-fix-incompatibleclasschangeerror-for-your-groovy-projects-running-on-jdk7
Fixes #1 scanner memory dumping often

It appears that if an exception is thrown during callback to a portal that the
outputstream of the connection may not be getting closed and GCd leading to a
memory leak. Have added some `finally` blocks to explicity close output streams
in the portal callback service.
Merge pull request #2 from aodn/issue-1

Fix for Issue 1