The NPOIFS-classes result currently in left-over memory mapped buffers.

The NPOIFS-classes result currently in left-over memory mapped buffers.
These are actually hard to workaround, so for Windows the test is ignored, if this error happens.
http://stackoverflow.com/questions/3602783/file-access-synchronized-on-java-object

Apart of that, the RandomFileAccess instance is saved in the FileBackedDataSource as it needs to
be closed instead of the Channel.
http://bugs.java.com/bugdatabase/view_bug.do?bug_id=4796385

git-svn-id: https://svn.apache.org/repos/asf/poi/trunk@1592418 13f79535-47bb-0310-9956-ffa450edef68