Returning null from a constuctor is silly

Throw an error instead.  This should help DigitalMan debug his issue.

exec/load/recordfile.js

@@ -71,7 +71,7 @@ function RecordFile(filename, definition)
 	this.RecordLength=getRecordLength(this.fields);
 	// A vbuf of a record length prevents more than one record from being in the buffer.
 	if(!this.file.open(file_exists(this.file.name)?"rb+":"wb+",true,this.RecordLength)) {
-		return(null);
+		throw new Error("Failed to open file "+this.file.name);
 	}
 	Object.defineProperty(this, 'length', {
 		enumerable: true,