The idea of the block indeed came from you paris.
But the "Join a group" block was based on code released under GPL (see Groups module code).
I know this since i helped you with the code and the complex SQL queries inside the block.
Since GPL states that code based on other code must be GPL this means the "Join a group" block is GPL.
Since you provided the block to use and that it included a notice about GPL, we may use it for any OpenSource purpose we want.
Due to that i added it to the CVS so that others may use it as well under the terms and conditions of the GPL.
Since i commited it to CVS the auto tag of the CVS program, $Author$ automaticly hooks the name of the commiter to the file so that others know who commited a revision of the file.
Since you're not satisfied that you're name is missing we could add a notice in the block itself (instead of only on this page) so that credit is given to you.