shp2pgsql-gui should warn when SRID is not specified

[bmmpxf]

When the SRID field is -1, and you click "Import" I'd like to see a popup saying, "You have not specified an SRID. Are you sure you wish to proceed?" Or something like that.

This may be too much handholding, but I think the issue of importing shapefiles and forgetting to enter in the SRID and then having to back out and start over is common enough in my experience (especially for novices, who are most likely to use this tool anyway) to warrant a little bit of a flag.

[strk]

Even better don't allow any explicit SRID <= 0 but rather have a checkbox to check if the user is really willing not to enter a SRID (ok to warn if checkbox is checked, eventually)