_copy_meta_inf: accept all legal base file names

[dnet]

As the documentation states:

If the alias name contains any characters that are not allowed in a signature file name, each such character is converted to an underscore ("_") character in forming the file name. Legal characters include letters, digits, underscores, and hyphens.

This commit adds the missing part to the regex: digits, underscore and hyphen, so that all key names are covered, otherwise there could be multiple signature files, resulting in confused verifiers.

[leonjza]

Thanks!