maintcheck: fix some failures, extend some checks

maintcheck: fix some failures, extend some checks

* Makefile.am (sc_diff_automake_in_automake): Update, as we
now expect 9 lines, not 8, to be changed from `automake.in'
to `automake'.
(sc_diff_aclocal_in_aclocal): New maintainer check, similar to
the above, and checking that only 10 lines are changed from
`aclocal.in' to `aclocal'.
(syntax_check_rules): Update.
(sc_tests_Exit_not_exit): Exempt self tests `self-check-*.test'
from this check, as they can legitimately use the bare `exit'
builtin in various places.
* doc/automake.texi (Python): Remove stray `@' from the end of
a line.  Typo introduced in commit `v1.11-312-g5bf7af6'.
* tests/depcomp8a.test: Pass DISTCHECK_CONFIGURE_FLAGS to make
from the environment rather than from the command line, to
pacify the `sc_tests_overriding_macros_on_cmdline' maintainer
check.
* tests/depcomp8b.test: Likewise.