Remove architecture normalization

ELF and RPM architectures are now distinct types in the database.
This better reflects reality, and should not cause any problems
because the two tend to be separate anyway.
Add build_host and build_time columns to symboldb.package
hash_sink: add MD5 support, to_string() and from_string() for hash types
checksum: Switch type member to hash_sink::type
rpm_load: Update FIXME
checksum::set_hexadecimal(): throw on error
Add additional test RPM

This RPM file contains a hardlink: /usr/bin/unzip and /usr/bin/zipinfo