Disk label corruption

[Steve Mynott]

I had last night a panic on the console with the CVS checkout of last
Thursday (no VFS changes from DragonFly-Stable).

Unfortunately I failed to make an exact note of the traceback this
time but it was a "vfs_cache" error"with something about malloc being
exhausted.  One disk was unaffected but the another seemed to lose its
disklabel with "no magic" on partition errors.

In hindsight I wish I had saved the disklabels for the disks (which I
have done now!)

If the problem happens again I will send a traceback.

Cheers Steve