testsuite: various fixlets and tweakings

testsuite: various fixlets and tweakings

* tests/seenc.test: Make grepping of automake stderr stricter.
Add a trailing `:' command.
* tests/symlink.test: Likewise.  Also, define `$am_create_testdir'
to "empty" to avoid bringing in unused auxiliary files (only to
have to remove them right away), and use proper m4 quoting in
`configure.in'.
* tests/vpath.test: Make grepping of generated `Makefile.in'
slightly stricter.  Prefer trailing `:' over trailing `Exit 0'.
* tests/suffix6c.test: Unset OBJEXT to avoid interferences from
the environment.
* tests/suffix12.test: Do not whitespace-indent `##' comments
when they are embedded in a makefile rule: having them indented
is not part of the Automake API, and might cause failures with
e.g., Tru64 make.
* tests/syntax.test: Simplify the `Makefile.am' to ensure that
automake doesn't fail for the wrong reasons.  Make grepping of
automake stderr slightly stricter.
* tests/test-harness-vpath-rewrite.test: Remove useless variable
definition from `Makefile.am'.
* tests/test-driver-custom-multitest.test: Fix typo in comments.
* tests/self-check-me.tap: Fix minor typo in test description.
* tests/vars3.test: Make grepping of automake stderr stricter
and safer.
* tests/version6.test: Add sanity check, verifying that the
version number extracted from `automake --version' output seems
legit.
* tests/auxdir2.test: Renamed ...
* tests/auxdir-compauted.tap: ... to this, and converted to the
use of TAP.
* tests/auxdir4.test: Renamed ...
* tests/auxdir-unportable.tap: ... to this, and converted to the
use of TAP.
* tests/auxdir3.test: Renamed ...
* tests/auxdir-misplaced.test: ... to this.
* tests/auxdir5.test: Renamed ...
* tests/auxdir-nonexistent.test: ... to this.
* tests/auxdir9.test: Renamed ...
* tests/auxdir-autodetect.test: ... to this.
* tests/Makefile.am (TESTS): Update.
(XFAIL_TESTS): Remove `auxdir2.test'.