[Swan-dev] functions that sometimes assign to an argument

[D. Hugh Redelmeier]

One of the hard tasks in understanding a program is to figure out who 
initializes a variable.

Some of our functions take pointer arguments so that the function can set 
a variable.

In many cases, the code would be easier to understand if the function 
always set that variable.

An example that I've not yet understood is resolve_default_route_one.  It 
sometimes resolves *peer and sometimes doesn't.  Who else would resolve 
it?  What if the results differ?  It would be simpler if only one bit of 
the program did that resolution.

Sometimes resolve_default_route_one is called twice with the same
arguments (if the result of the first call is 1).  I think that it
will resolve *peer in both calls.