davautocheck.sh: use the APXS value from Makefile.  Without this patch,
/usr/bin/apxs2 would be used even if --with-apxs=... was passed to configure.

I think the
 || APXS=$(which apxs) \
 || APXS=$(which apxs2) \
lines may be removed now, too.

* subversion/tests/cmdline/davautocheck.sh
  (APXS): Sniff the value from Makefile.  Since this depends on $ABS_BUILDDIR,
    move the code that sets that variable up (without changing it).

git-svn-id: https://svn.apache.org/repos/asf/subversion/trunk@1507889 13f79535-47bb-0310-9956-ffa450edef68