Modernize, improve and/or fix various test scripts.

Modernize, improve and/or fix various test scripts.

* tests/symlink3.test: Deleted, separated into two new, more
complete tests ...
* tests/forcemiss.test: ... this one ...
* tests/forcemiss2.test: ... and this one.
* tests/symlink2.test: Enable `errexit' shell flag, make test
stricter, and skip it if symlink creation is not supported.
* tests/postproc.test: Enable `errexit' shell flag, related
changes, and a couple of unrelated cosmetic changes.
* tests/recurs.test: Use the `configure.in' stub created by
`./defs', rather than writing one from scratch.  Make grepping
of Automake stderr slighty stricter.
* tests/substtarg.test: Likewise.
* tests/strip.test: Likewise, and move the call to `set -e'
earlier (just after the inclusion of `./defs').	Also, make sure
that the script installed by `make install-script' is equal to
the original one.
* tests/substref.test: Use the `configure.in' stub created by
`./defs', rather than writing one from scratch.  Move the call
to `set -e' earlier (just after the inclusion of `./defs').
Avoid to explicitly export CC for configure (that's already done
in ./defs).  Avoid potential problems with unpredictable make
output.  Finally, make grepping of Makefile.in stricter.
* tests/substre2.test: Ensure verbose printing of the captured
make's output, and make its grepping slighty stricter.
* tests/cygwin32.test: Enable `errexit' shell flag, and related
changes.  Also, do not create useless dummy source/data files.
* tests/scripts.test: Likewise.
* tests/recurs2.test: Likewise.  Also, use the `configure.in'
stub created by `./defs'.
* tests/Makefile.am (TESTS): Updated.

Signed-off-by: Ralf Wildenhues <Ralf.Wildenhues@gmx.de>