Hi and thanks for the contributed module.
With the original info file uc_check_stock_before_cart is located in the modules node in other.
This changes are just to insert the module into the Ubercart extra package and adding the version number:
Save this lines in: uc_check_stock_before_cart.info
name = Check Stock Before Cart
description = Checks the stock levels of the attributes selected before adding the product to the cart.
version = "6.x-1.0"
core = 6.x
package = "Ubercart - extra"
project = "ubercart"
datestamp = "1320511440"