Tweak behavior of FileUtils.getFileExtension.
Tweak behavior of FileUtils.getFileExtension.

This change avoids creation of superfluous java.io.File objects.

This used to be revision r4338.

biovoxxel/imagej,TehSAUCE/imagej,TehSAUCE/imagej,TehSAUCE/imagej,biovoxxel/imagej,biovoxxel/imagej