#1 Command-line switch to stay on one device

[Arnout Engelen]

This patch adds the '--onedev' command-line switch,
which prevents fsv from scanning directories that are
not on the same device.

This is particulary useful when you have a filesystem
that you want to clean up to make space, and are
wondering what is taking up so much space. Partitions
mounted onto this filesystem will not be scanned.

[Arnout Engelen]