Automate regression testing of the XML/XSLT implementation. Discussed

Automate regression testing of the XML/XSLT implementation.  Discussed
starting at
<http://lists.gnu.org/archive/html/bison-patches/2007-11/msg00021.html>.
* configure.ac (XSLTPROC): New substitution.
* Makefile.am (maintainer-xml-check): New phony target invoking...
* tests/Makefile.am (maintainer-xml-check): ... this new phony target
invoking make maintainer-check with BISON_TEST_XML=1.
* tests/atlocal.in (XSLTPROC): New.
* tests/local.at (AT_BISON_CHECK): New macro to (1) instruct Valgrind
not to report reachable memory when Bison is expected to have a
non-zero exit status and (2) to compare XML/XSLT output with --graph
and --report=all output for every working grammar when
BISON_TEST_XML=1.
(AT_BISON_CHECK_NO_XML): Likewise, but skip XML checks.
(AT_BISON_CHECK_XML): New.
(AT_QUELL_VALGRIND): New.
* tests/testsuite.at (ORIGINAL_AT_CHECK): Remove this and...
(AT_CHECK): ... don't redefine this since this was the old way to
quell Valgrind.
* tests/actions.at: Rewrite all AT_CHECK invocations for bison as
AT_BISON_CHECK invocations.
* tests/c++.at: Likewise.
* tests/calc.at: Likewise.
* tests/conflicts.at: Likewise.
* tests/cxx-type.at: Likewise.
* tests/existing.at: Likewise.
* tests/glr-regression.at: Likewise.
* tests/headers.at: Likewise.
* tests/input.at: Likewise.
* tests/java.at: Likewise.
* tests/output.at: Likewise.
* tests/push.at: Likewise.
* tests/reduce.at: Likewise.
* tests/regression.at: Likewise.
* tests/sets.at: Likewise.
* tests/skeletons.at: Likewise.
* tests/synclines.at: Likewise.
* tests/torture.at: Likewise.
(Big triangle): Use AT_BISON_CHECK_NO_XML instead since this grammar
tends to hang xsltproc.
(Big horizontal): Likewise.