fidefrag should use ionice

[Kamil Páral]

Fidefrag is very harddisk intensive. For example on my laptop I can't use Firefox while running fidefrag. Fidefrag should use ionice to have lower priority when accessing disk. Or a commandline option to set it may be a good idea. This option could run something like "ionice -c2 -n7" or maybe even better "ionice -c3". This way users can work along with using fidefrag.