Improve, extend and tweak tests on Texinfo support. * tests/instdir-texi.test: Add a call to `ls -l' after that to `make', for debugging. When looking for required tools, do not redirect the output of "$tool --help" to /dev/null, and do not uselessly run it in a subshell. * tests/txinfo.test: Rewritten to run autoconf, ./configure and make. All checks moved into Makefile.am. * tests/txinfo8.test: Likewise, and modernize the generated configure.in. * tests/txinfo2.test: Moved checks into Makefile.am, and other minor improvements. * tests/txinfo5.test: Enable `errexit' shell flag, and related changes. Add trailing `:' command. * tests/txinfo6.test: Likewise, and make grepping of generated Makefile.in stricter. * tests/txinfo7.test: Enable `errexit' shell flag, and related changes. Add trailing `:' command. Do not add unnecessary stuff to Makefile.am. * tests/txinfo9.test: Verify that more targets which are expected to be generated only once really are. Make grepping less strict, to avoid exposing too much internal details. More minor changes. * tests/txinfo16.test: Add trailing `:'. Prefer cat over echo for appending to configure.in. Updated/fixed heading comments. * tests/txinfo23.test: Likewise, and extended a little by making it check that no info file is created in the $(srcdir). * tests/txinfo24.test: Likewise. * tests/txinfo25.test: Likewise. * tests/txinfo18.test: Add trailing `:'. Prefer cat over echo for appending to configure.in. Also, check that index files are cleaned also by "make clean", not only by "make distclean". * tests/txinfo22.test: Prefer `$me' over hard-coded test name, and added trailing `:' command. This testcase also used to check that automake ignores in-line comments when using variables, but preserves them in the output; these checks (added in commit "Release-1-7f-4-g9177ef8") do not really pertain to this test, so they have been moved ... * tests/comments-in-var-defn.test: ... into this new test. * tests/txinfo4.test: Escape literal dots in grep regexps. Add trailing `:' command. * tests/txinfo29.test: Likewise. Relax grepping of generated Makefile.in w.r.t. whitespaces. Prefer `cat' over `echo' to append to configure.in. * tests/txinfo3.test: Likewise. * tests/vtexi.test: Improve grepping of Makefile.in (sometimes make it stricter, sometimes laxer). Move `set -e' setting just after the inclusion of ./defs. De-uglify a sed command. Other minor cosmetic improvements. * tests/vtexi2.test: Make grepping of Makefile.in stricter. Add trailing `:' command. * tests/vtexi3.test: New test on version.texi support. * tests/vtexi4.test: Likewise. * tests/Makefile.am (TESTS): Updated.