The repodata archive wasn't group writable, resulting in a new archive
created from scratch if the fd wasn't writable.
repodata archives are now created with 0664 mode, this way its main group
also can write to it.
- Removed -c --clean mode. It's not too useful and adds a considerable
amount of gratuitous code. It takes almost the same time than
adding all pkgs from scratch.
- When creating the repository data always add the meta plist at the
2nd position in the archive, to optimize its access.
- Misc improvements.
The list of required external deps is now confuse, libarchive and openssl.
libxbps now includes a wrapper for proplib prefixed with xbps_ rather than prop_.
