Fix tests when building out-of-tree

(This was too hard. Silly autoconf.)

configure.ac

@@ -1407,6 +1407,14 @@ AC_SUBST(BINDIR)
 LOCALSTATEDIR=`eval echo $localstatedir`
 AC_SUBST(LOCALSTATEDIR)
 
+case "$srcdir" in
+  /*) TOP_SRCDIR=$srcdir;;
+  *) TOP_SRCDIR=$PWD/$srcdir;;
+esac
+
+AH_TEMPLATE([TOP_SRCDIR],[source directory we're building from])
+AC_DEFINE_UNQUOTED(TOP_SRCDIR,"$TOP_SRCDIR")
+
 if test "$bwin32" = true; then
   # Test if the linker supports the --nxcompat and --dynamicbase options
   # for Windows

src/test/test_entrynodes.c

@@ -115,7 +115,7 @@ static void *
 fake_network_setup(const struct testcase_t *testcase)
 {
   /* This is the file containing our test descriptors. */
-  const char *fname = BUILDDIR "/src/test/test_descriptors.txt";
+  const char *fname = TOP_SRCDIR "/src/test/test_descriptors.txt";
 
   (void) testcase;