Generic build script instructions

[Robb, Sam]

> > :  I think we could use something like "make -n" and check the return code...
> > :  But as I don't have the time to implement it properly now, I'll look at
> > :  whatever methods people choose to provide in their patches.
> >
> > It was something using a ``make -f -'' IIRC... (l8r)
> 
> Hmm, "make -f -" will actually not be useful, FWICS.  We want to check
> whether the Makefile contains either a "test" or a "check" rule, whereas
> "make -f -" will bypass the Makefile altogether.  But if I'm wrong, it
> won't be the first time.

... but not this time, at least :-)  Assuming that there's nothing else wrong with
the makefile, "make -n target" will return != 0 if target does not exist (assuming
that there isn't an explicit call to $(error) or similar).
 
-Samrobb