Why xmlsitemap table id is not autoincrement ?

Hello !!

I've just install xmlsitemap (and xmlsitemap_custom) to create my sitemap.
It works fine, but i want to create a script to insert custom links by running a hook_update.
And db_insert query abort, cause of duplicate key in xmlsitemap table.
So I check hook_schema, and xmlsitemap id is an integer, but no autoincrement..

Is there a reason for that ?

Here is a little patch to make this field autoincrement !!