NetworkManager dependency

[Ethan Blanton]

Michael McConville spake unto us the following wisdom:
> Jorge Villaseñor wrote:
> > Michael McConville wrote:
> > > Is there a reason why ./configure fails on machines without
> > > NetworkManager unless it's explicitly disabled? Many (most?)
> > > platforms don't have it.
> > 
> > Are you proposing change the "enable by default" to "disable by
> > default" for linux-specific options?
> 
> I'm suggesting making it "enabled if available": use it if it's there,
> but don't fail the build in its absence unless the user configured with
> --enable-nm.

We moved almost everything to either flat out enabled or flat out
disabled by default a few years ago, because people were building
Pidgin and being surprised by the configuration they got.  This way
the configuration is fairly well-known unless you --enable or
--disable certain things.

> I might be mistaken, but I think other stuff is configured like that.
> Cyrus SASL comes to mind.

There may be a few things.  There shouldn't be many, for the above
reason.

Network manager is something that often causes more trouble than it's
worth, anyway, and we speak an ancient protocol to boot.  (In fact,
newer protocols fix some of the troubles we see, I believe.)  It may be
reasonable to disable-by-default.

Ethan