TAP driver: remove perl implementation (move it into contrib/)

TAP driver: remove perl implementation (move it into contrib/)

That implementation was only meant as a standard against which the
portable awk+shell implementation was to be measured.  Now, since
Automake 1.12, the latter implementation is fully functional and
already used in the wild, and in fact feature-par with the perl
implementation.  So the perl implementation is now just slowing
down and complicating our testsuite.  Let's move it to 'contrib/'
(we don't want to remove it, in case someone is actually using it
in the wild).

* lib/tap-driver.pl: Move it ...
* contrib/tap-driver.pl: ... here.  While at it, convert quoting
`like this' to quoting 'like this', and remove an obsolescent FIXME
comment.
* lib/Makefile.inc (dist_script_DATA): Drop '%D%/tap-driver.pl'.
* Makefile.am (EXTRA_DIST): Add 'contrib/tap-driver.pl'.
* doc/automake.texi: Remove one stray reference to 'tap-driver.pl',
and reference 'tap-driver.sh' instead, as intended.
* t/ax/am-test-lib.sh ($am_tap_implementation): Delete definition and
uses.
(fetch_tap_driver): Simplify to unconditionally assume the shell+awk
implementation of the TAP driver is used.
(get_shell_script): Make more flexible so that it can cater to the
needs of 'fetch_tap_driver()'.
* t/tap-bad-prog.tap: Likewise.
* t/tap-bailout-leading-space.sh: Likewise.
* t/tap-signal.tap: Likewise.
* t/tap-test-number-0.sh: Likewise.
* t/test-driver-cond.sh: Use 'tap-driver.sh' instead of 'tap-driver.pl'.
* gen-testsuite-part (%test_generators): Do not generate sister tests
that use the perl TAP driver rather than the shell+awk one.
* NEWS: Update.

Signed-off-by: Stefano Lattarini <stefano.lattarini@gmail.com>