Provide notice when taxa upload fails

[jbest]

When attempting to upload taxa in a local development instance, I ran into a number of problems where the upload fails but the web interface doesn't indicate a failure. I was uploading an ITIS format taxonomy file at Symbiota/taxa/admin/taxaloader.php and this failed repeatedly due to my local PHP configuration but this was hard to diagnose since the web GUI didn't indicate when or why the upload failed.