'Update the checksum of the package in the packages\' checksum
file. This method is called whenever a package is fetched just
to be sure that the checksums in the local file are the latest.
pkg_path : The complete path to the package file.'

def update_checksum(self, pkg_path):

    new_checksum = self.compute_checksum(pkg_path)
    checksum_dict = self._get_checksum_dict()
    checksum_dict[os.path.basename(pkg_path)] = new_checksum
    self._save_checksum_dict(checksum_dict)
