bug#19438: 24.4; system-name bad cache

[Paul Eggert]

Stefan Monnier wrote:
> Maybe we could make the system-name function return the same as
> `hostname` (and do it dynamically).

OK, thanks, I revised the patch to do that, and made the var obsolete, and 
installed something along those lines into the master.  (It was 3 patches not 
one because I installed the wrong version first, sorry.)  Marking this as done.