Seeing `g.add_drive_opt :readonly => 1` allows one to imply
that ensuring writable access to drive should happen via
`g.add_drive_opt :readonly => 0`. However, the passed option
value gets passed down to C according to Ruby Boolean semantics,
that is, any value apart from `false` and `nil` will be true
(see RTEST in Ruby C API).
So its more idiomatic and provides a better hint if we use
`g.add_drive_opt :readonly => true` in Ruby samples.
In libguestfs 1.20, you will be able to use 'add_drive'
instead of 'add_drive_opts' (except in the C bindings).
However until libguestfs 1.20 is the minimum stable version
people will still be using old versions where you have to use
'add_drive_opts'. This makes the examples confusing.
Therefore continue to use 'add_drive_opts' in the examples
for now.
By using the once_had_no_optargs flag, this change is backwards
compatible for callers (except Haskell, PHP and GObject as discussed
in earlier commit).
Fix guestfish (and other C tools) so that they ignore errors
when /etc/fstab contains bogus entries.
Update the documentation for inspect-get-mountpoints to emphasize
that callers must be aware of this when mounting the returned
values.
Add a regression test.
Update the example code ("inspect_vm") to reflect the way this
API ought to be called.
For more detail see:
https://bugzilla.redhat.com/show_bug.cgi?id=668574
