Every devicescan now tests on beforehand if the kernel is able to reread

* Every devicescan now tests on beforehand if the kernel is able to reread the partitiontable. If the kernel is unable to do
  this, i disallow most operations. This may seem weird and even a bad thing to do, but the fact is it protects
  the innocent user from a lot of potential damage. Till the linuxkernel is able to reread partitiontables no matter what, this seems
  to be the best option. Of course a dialog with information will popup whenever such a situation is encountered.
  In a next release i might consider adding an 'advanced mode' for users who know what they're doing.