The storage pools page contains details about the capabilities of the
various pool types, but not an overview of how they are intended to be
used.  This patch adds some explanation of what pools and volumes can
be used for and why an administrator might want to use them.

Got sick of seeing the "validity error : ID Objects already defined"
errors, which this patch addresses.

  msdos patch and apply new one from Cole Robinson
daniel

* docs/storage.html[.in] src/storage_backend_disk.c: patch from
  Cole Robinson to rename the disk type from 'dos' to 'msdos'
Daniel