have configure generate header dependencies automatically

[Carson Gaspar]

Corinna Vinschen wrote:
...
> I don't know if that's helpful, but there's also the gcc -MMD option to
> create local dependencies per compilation unit.  It's pretty easy to use
> in Makefiles.

And is entirely gcc-specific. For those of us who don't build with gcc, 
please don't. Or rather please make it optional if you do.

-- 
Carson (who just had to take a weed whacker to some Makefiles last night 
because of this)