xenstore-ls -f for find(1)-like output

xenstore-ls -f for find(1)-like output

The current output of xenstore-ls can be quite hard to read and it is
not very intractable for postprocessing with sort|diff and the like.

The patch below provides a -f option which produces output with the
full key pathname on each line, and which disables the value
truncation and the `.'-padding when used with -p (since these latter
two aren't likely to be very useful when values are preceded by long
pathnames).

While I was at it I added the `-s' option to the usage message, where
it was previously missing.

The results looks like this:

...
/local/domain/1 = ""
/local/domain/1/vm = "/vm/8b5fd34a-e268-fab5-9cde-c06eda21df16"
/local/domain/1/device = ""
/local/domain/1/device/vbd = ""
/local/domain/1/device/vbd/2049 = ""
/local/domain/1/device/vbd/2049/virtual-device = "2049"
/local/domain/1/device/vbd/2049/device-type = "disk"
/local/domain/1/device/vbd/2049/protocol = "x86_32-abi"
...

Signed-off-by: Ian Jackson <ian.jackson@eu.citrix.com>