Ignored Sandbox
Handle inexistent devices

 If a device is unplugged without prior unmounting, it still
 appears in the /etc/mtab file, which is used for this monitor.
 The problem is that this monitor canonicalized every path
 regardless of whether it actually existed or not. I basically
 added the 'only canonicalize if file exists'.
Merge remote-tracking branch 'rethab/master'