fixed VirtualEntryIterator bug not returning the first element.
Fixed NullPointerException inside VirtualDiskUtil.

Added check if the directory has any members at all.
VirtualDiskTest uses now VirtualDiskUtil for testing
Added package-info.java to ch.se.inf.ethz.jcd.batman.vdisk.util
removed printStackTrace call

is an artifact of some testing I've done.
fixed bug: input line started always with output prefix.
removed unused imports