Disallow merging variable name with keywords

[wipe2238]

procedure proc(variable &end)
begin&end++;
  if&end>10then&end=-1; return &end;
end

All vars should follow same syntax rules; having a way to have very unique var name is real nice (for example when global scope variable is defined deep down in header), fact that it introduces own subset of syntax rules is not :/

Disallowing merging constants with keywords would be nice too~