some linting on function definitions

some linting on function definitions

* instead of empty args "void" should always be specified.
  Using this, the compiler can detect incorrect function calls,
  like with update_stuff().
* No args seems to be interpreted as "unspecified args" by the
  compiler, as with update_mail_count(). So no checking for
  correctness of arguments when calling was done at all.
* This is not complete yet, as I still don't have any BSD for
  testing.

git-svn-id: https://conky.svn.sourceforge.net/svnroot/conky/trunk/conky1@1055 7f574dfc-610e-0410-a909-a81674777703