[O] [babel] java headless support is missing for most graphing languages

[Mikhail Titov]

Hello!

I’ve noticed that at least ditaa and plantuml fail to evaluate with babel.

While for ditaa I can override :java list item with something like

(setq org-babel-default-header-args:ditaa
  '((:results . "file")
    (:exports . "results")
    (:java . "-Dfile.encoding=UTF-8 -Djava.awt.headless=true")))

However plantuml is handling differently. Curiously enough it runs just fine 
without stdin/stdout redirection from the command line. However if I tried to 
use input/output redirection like in ob-plantuml.el , it complains like the 
following:  Exception in thread "main" java.lang.InternalError: Can't connect 
to window server - not enough permissions.

I propose to add by default “-Djava.awt.headless=true” to all “language” 
handlers supported by org-babel. I think it won’t hurt and will make working 
from CLI more enjoyable out of box.

Mikhail