Extend and improve tests on DejaGnu support.

Extend and improve tests on DejaGnu support.

* tests/dejagnu.test: Do not create useless dummy test script.
Add trailing `:' command.  In heading comments, add reference
to ...
* tests/check12.test: ... this new "semantic" test, covering
concurrent use of dejagnu tests, simple tests and `check-local'
target.
* tests/dejagnu2.test: Make test more reliable, by avoid weak
grepping of make output.  Prefer `cat' over `echo' to append
to configure.in.  Quote literal dots in grep regexps.  Prefer
`grep -c ...' over `grep ... | wc -l'.  Make grepping of
automake stderr slightly stricter.  Add trailing `:' command.
* tests/dejagnu3.test: Prefer `cat' over `echo' to append to
configure.in.  Check stderr of expected-to-fail "make" call.
Remove extra blank lines from Makefile.am.
* tests/dejagnu4.test: Prefer `cat' over `echo' to append to
configure.in.  Prefer `mv -f' over plain `mv' when the target
file already exists.  Avoid extra mkdir calls by creating more
directories at once.  Better use of blank lines.  Check that
the `*.log' and `*.sum' files are created by runtest also when
"make check" fails.
* tests/dejagnu7.test: Prefer `cat' over `echo' to append to
configure.in.  Better use of blank lines.  Add a trailing `:'
command.
* tests/dejagnu6.test: Likewise, and give the dejagnu test a
more descriptive name.
* tests/dejagnu5.test: Likewise.  Also, simply define package
name to `$me' rather than using a non-obvious sed script to
extract it from `AC_INIT', and write the Makefile.am with only
one command.
* tests/Makefile.am (TESTS): Updated.