Sources renaming is not supported

Hi,

particularly when pulling something from github tags (like i do in one of the packages i manage on the AUR) it's useful to rename sources (see [here](https://wiki.archlinux.org/index.php/PKGBUILD#source)).
Currently this mode does not support source renaming: the pkgbuild-source-check function fails in finding those files. It's possible to add the functionality to this mode?