Remove compile warnings about corb2 HOT 1 CLOSED

Mads,
Could you please look into other warnings when you get a chance. I am not sure if these changes require a new release. The scanner resource leak (in master branch) for windows in HostKeyDecrypter has a minimal effect as we are closing the underlying the buffer reader anyway. Also, HostKeyDecrypter is called only once at the start (if used)

I made couple of changes in development branch (below) -

1. Changed the function PostBatchUpdateFileTask.getComparatorCls function to return Comparator and suppressing warnings for typecast as I couldn't find a better way to do it.
2. In HostKeyDecrypter, scanner doesn't implement closeable in java 1.6. So, I changed the code to call close instead of FileUtils function.

from corb2.