whitespace
Don't use "return" in a comment, it messes up the style check.
Change the data-source create method signature to take a char *[]cfg,
not a char *config, for consistency.   This should really be done at
a higher level throughout the source, but I'm just clipping it at an
easy spot for now.
Support the cursor overwrite flag in data-source cursors.
There's no way to reconfigure a cursor at run-time in the current system;
add a comment noting that if a way is added in the future, we need to add
a similar call to data-source cursors, or, disallow reconfiguration.
User-specified collators aren't supported for data-source objects,
catch the error.