volinfo: accept -sizeonly for -sizeOnly

For consistency, allow -sizeonly (all lowercase letters) to
request the size summary. The old option name, -sizeOnly is
available as an alias.

Define the command line option parameter positions and use
those to set and look up the options.

1.6 note: The libcmd in 1.6 lacks parameter aliases and offsets.
Instead we create params the normal way and make the offsets enum line
up with the default offsets. To get an alias for -sizeonly, we create
a new parameter that just does the same thing (P_SIZEONLY_COMPAT).

Reviewed-on: http://gerrit.openafs.org/4741
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Derrick Brashear <shadow@dementia.org>
(cherry picked from commit 1a4262253e78aa7a4e8c58006abd3301f71bab89)

Change-Id: Ic630a7c0b29bd62525dd2211a7771c647e1be8df
Reviewed-on: http://gerrit.openafs.org/11258
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Andrew Deason <adeason@sinenomine.net>
Reviewed-by: Stephan Wiesand <stephan.wiesand@desy.de>