pack_default_options(+Spec, -Pack, +OptionsIn, -Options) is det[private]

Establish the pack name (Pack) and install options from a specification and options (OptionsIn) provided by the user. Cases:

1. Already installed. We must pass that as pack_default_options/4 is called twice from pack_install/2.
2. Install from a URL due to a url(URL) option. Determine whether the URL is a GIT repository, get the version and pack from the URL.
3. Install a local archive file. Extract the pack and version from the archive name.
4. Install from a git URL. Determines the pack, sets git(true) and adds the URL as option.
5. Install from a directory. Get the info from the packs.pl file.
6. Install from '.'. Create a symlink to make the current dir accessible as a pack.
7. Install from a non-git URL Determine pack and version.
8. Pack name. Query the server to find candidate packs and select an adequate pack.