[gforth] x and y words exposed

[Ethan Gardener]

i've been defining variables x y z in my startup file for a while now, but 
recent versions of gforth report a redefinition warning for x and y.  ("recent" 
is from late 2018, perhaps october.)  the conflicting definition for x is 
reported to be:
    current/unix/jni-helper.fs:80:1
line 81 conflicts with y.

i'm surprised at such short names being globally exposed, especially from 
something which seems quite optional; the comment at top of file reads, 
"show/hide keyboard using jni tools".  should i care about this?  is the only 
problem the untidy warning on startup, or could it hinder my use of jni 
features?  if i ever get that far. :)