[ng] recheck: don't exceed command line limits, even with many failed tests

[ng] recheck: don't exceed command line limits, even with many failed tests

Related to automake bug#7868.

* lib/am/parallel-tests.sh (recheck): Arrange recursive make invocation
to pass the list of tests to be rechecked in the make standard input
rather than on the make command line.
(am__test_bases): Only define if not already set, to make the new idiom
referenced above work as expected.
* Makefile.am (XFAIL_TESTS): Remove 't/parallel-tests-many.sh' once
again.

Signed-off-by: Stefano Lattarini <stefano.lattarini@gmail.com>