pack_install: make pack_install(Spec) directly use pack_install(Spec, [])?

[rla]

Currently pack_default_options/4 is run twice when using pack_install/1 which causes some issues:

https://groups.google.com/forum/#!topic/swi-prolog/HYYATv_70u0

Maybe it would be best to just define pack_install(Spec):- pack_install(Spec, []).

[JanWielemaker]

That is probably what it should become. Originally, the idea was that pack_install/1 would take anything that hinted at a pack, get what the user wanted and run pack_install(Pack, +Options) to do it. It is now a bit in the middle :-( For now I just hacked around it. Too many more interesting things to do ...