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
