If specified, validate package alias

[joliver]

When specifying an alias for a package. e.g. "haproxy", ensure that the alias provided is found as a substring in at least one of the dsc/deb files indicated.

[joliver]

The name of the package alias should be contained in the prefix or suffix of at least one of the binary/source package names, e.g.

vim-haproxy (found in the suffix)
nginx-full (found in the prefix)