[Dune] m4 cleanup

[Christian Engwer]

Hi Elias,

> I've taken a stab at cleaning up the m4/dune*.m4 files from
> dune-common, (following [1], mostly) replacing if-clauses w/ AS_IF,
> AC_HELP_STRING w/ AS_HELP_STRING, and fixing a bug or two
> (with_parallel -> enable_parallel).

Thanks for your patch. Most of it seems fine, there is just one part
of your changes where I'm not so sure about.

Let me pick out one example:

> -  if test "x$with_hostid" = "xno" ; then 
> -    with_hostid="$ac_hostname (`uname -sm`, $COMPILER_NAME)";
> -  fi
> +  AS_IF([test "x$with_hostid" = "xno"],[
> +    with_hostid="$ac_hostname ($(uname -sm), $COMPILER_NAME)";
> +  ])

You changed backticks to $(). $() is a bashism and `` is posix-sh. As
the autotools create a sh-script and not bash I'm a little bit
surprised. Does automake/autoconf replace these constructions?
Otherwise I think `` is the safer way to do it. What was the reason
for this particular change?

Cheers Christian