... instead of a low precedence unary operator with an odd
behaviour. This wasn't documented nor specified but maybe needed
for old(est) binary file format compatibility. Generate an error
for anything else than a context of a function with one argument.

There might be some corner cases of documents where some old usage
leads to error now, of which some may have worked by accident, but
some not as intended.

Related, the internal not exposed (but available) NEG was classified
similar as a unary operator but corectly handled as function at all
places. Classified as an ordinary 1-parameter function as well.

Change-Id: I3d84a6382243c8d64313e37346f81c857e71be95
Reviewed-on: https://gerrit.libreoffice.org/50055Reviewed-by: Eike Rathke <erack@redhat.com>
Tested-by: Eike Rathke <erack@redhat.com>