t/Makefile: teach `make test` and `make prove` to run chainlint.pl

t/Makefile: teach `make test` and `make prove` to run chainlint.pl

Unlike chainlint.sed which "lints" a single test body at a time, thus is
invoked once per test, chainlint.pl can check all test bodies in all
test scripts with a single invocation. As such, it is akin to other bulk
"linters" run by the Makefile, such as `test-lint-shell-syntax`,
`test-lint-duplicates`, etc.

Therefore, teach `make test` and `make prove` to invoke chainlint.pl
along with the other bulk linters. Also, since the single chainlint.pl
invocation by `make test` or `make prove` has already checked all tests
in all scripts, instruct the individual test scripts not to run
chainlint.pl on themselves unnecessarily.

Signed-off-by: Eric Sunshine <sunshine@sunshineco.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>