tests: tweak and improve tests on "Simple Tests" driver

tests: tweak and improve tests on "Simple Tests" driver

* tests/check.test: Make grepping of generated Makefile.in
slightly stricter.  Add trailing `:' command.
* tests/check2.test: Ensure verbose printing of captured make
output.  Make grepping of generated Makefile.in and of make
output stricter.  Add trailing `:' command.
* tests/check3.test: Likewise.  Also, fix minor error in a
comment.
* tests/check4.test: Stricter grepping of make output.  Use
`using_gmake' subroutine instead of copy&paste from defs.in
to determine whether $MAKE is GNU make.  Add a trailing `:'
command.
* tests/check6.test: Add trailing `:' command.
* tests/check10.test: Prefer redirection `>' over `>>' when
creating new files.  Ensure verbose printing of captured make
output.
* tests/check11.test: Likewise.
* tests/check7.test: Likewise.  Make grepping of make output
stricter.  Prefer "make distcheck" over a simple "make check"
in a VPATH build. Add trailing `:' command.
(a.c): Format following GNU coding standards.
(Makefile.am): Explicitly declare target `print-xfail-tests'
as PHONY.  Distribute $(check_SCRIPTS), for distcheck.
* tests/parallel-tests.test: Prefer redirection `>' over `>>'
when creating new files.
* tests/parallel-tests2.test: Likewise.
* tests/parallel-tests9.test: Likewise.
* tests/parallel-tests8.test: Likewise.  Make grepping of
automake stderr stricter.
* tests/check8.test: Likewise.  Make formatting of created
*.c files more consistent with GNU Coding Standards.
* tests/check-subst-prog.test (configure.in): Break overly
long lines.
(pass-prog.c, xfail-prog.c): Format them more consistently
with GNU Coding Standards.
* tests/parallel-tests3.test: Use a shorter and clearer skip
message.  Use the `unindent' subroutine to improve readability
of indented loop bodies.  Simplify the hack used to please
maintainer-check.
* tests/parallel-tests5.test: Make formatting of created *.c
files more consistent with GNU Coding Standards.  Use the
`unindent' subroutine to improve readability of indented loop
bodies.
* tests/parallel-tests10.test: Add blank line, for clarity.
Prefer trailing `:' over trailing `Exit 0', for consistency
with other tests.