I just commited a "special_sqldump.php" file with a function that creates a
SQL dump as a zipped file in the upload directory each time it is called.
Runs about 21 sec on my system. I didn't link it from anywhere else yet, so
you'll have to access the page through "...../wiki/special:sqldump". After
it finished, you'll get a direct link to the file and a file size in KB.
Please have a look.
Magnus