set nargs to -1 for Application

The function log has nargs = (1, 2). It would be nice to remove
the nargs attribute from log(x) since the number of arguments is
exactly 1 -- len(log(x).args) == 1. But I haven't been successful
at that. So rather than leave nargs defined to either the unapplied
nargs value (a tuple) or redefining it as an integer equal to the
length of the functions args, it is being set to -1 to discourage
its use.