Sometimes (all the time?) hosts are "cloned" or deep-copied instead of being
copied by reference, so testing whether a host is "in" a scan is insufficient.
Now we check by address, the same way that Zenmap uses to determine 2 hosts are
the "same" for merging their output.
Also, avoid considering a scan as having unsaved changes if the comment field is
merely focused but unchanged.
41e06e9e9c