AC_CONFIG_LINKS breaks every second time

[Sebastian Freundt]

Hi all,
I've got a problem with a recent change in the implementation of
AC_CONFIG_LINKS.  It is now checked whether a symlink already exists, if
so it does really obscure things.  Here's a minimal example:

relevant parts of my source tree:
./src/s/

my build directory (distinct from $srcdir):
/home/src/=build/

There's an AC_CONFIG_LINKS([src/s:src/s]) in my configure.ac.
configure or config.status, respectively, now do the following:

1. in a clean build directory: create the src subdirectory, create the
   symlink from $srcdir/src/s to $builddir/src/s
2. in a configured build directory: delete $builddir/src/s and create a
   link from $builddir/src/s(!) to $builddir/src/s
3. in such a screwed build directory, another invocation of config.status
   yields the correct link again ($builddir/src/s -> $srcdir/src/s)

> From then on, steps 2 and 3 alternate upon calling config.status.

A quick look into config.status reveals the source of this bug:

  test -r "$ac_source" || ac_source=$srcdir/$ac_source

and irrespective of the actual state of $ac_source, it is tried to

  ln -s "$ac_source" "$ac_source"

which is of course complete non-sense!  I manually evalutated all the
variables to their final value to show the oddity.

Best wishes
Sebastian