This flag value can be used to indicate if a command has the property of
being "memory safe". In this instance, memory safe means that the
command does not allow/enable reads or writes of arbitrary memory,
regardless of the arguments passed to it. For example, 'backtrace' is
considered a memory-safe command since its output is deterministic,
while 'show vnode' is not, since it requires a memory address as an
argument and will print the contents beginning at that location.
Provide _FLAGS variants of the various command definition macros, so
that command definitions can be augmented with this new flag, and
conceivably any others they require.