[Kst] getData flexibility

[Eli Fidler]

I'm in the process of writing the new NAD KstDataSource with uses the local 
cache. I've run into a case of getData() where the current interface seems 
insufficient.

When using the NAD cache, I may have frames 1 to 50 of a particular field in 
the cache. If the NAD server connection is unavailable, what should I do if 
the user requests frames 1 to 100? What about 1 to 50?

I assume I should just give them the data in the second case and pretend 
everything is fine. In the first case, should I return partial data? no data? 
something else?

What if I have part of the data, but it's not the first part?

The problem stems from the fact that I can only return -1 for any error, so I 
can't signal a partial success very easily.

Eli