Add missing kvno options to the kvno.rst synopsis and option
descriptions, and to the kvno usage message. Remove mention of '-h'
(help text), from kvno.rst as it is an implicit option. Note that the
three new caching options were added in release 1.19.
Indicate the two exclusions (-u/-S and --u2u with the S4U2Self options)
and dependency (-P on S4U2Self) where they are missing.
Switch xusage() to print only a single localized string, rather than
running each line of output through localization separately.
Leave kvno -C undocumented for now, as the semantics of
KRB5_GC_CANONICALIZE are minimally useful and likely to change.