t/Makefile: always test all lint targets when running tests

Only the two targets "test-lint-duplicates" and "test-lint-executable" are currently executed when running the test target. This was done on purpose when the TEST_LINT variable was added in 81127d74 to avoid twisted shell scripting by developers only to avoid false positives that might result from the rather simple minded tests, e.g. test-lint-shell-syntax. But it looks like it might be better to include all lint tests to help developers to detect non portable shell constructs before the patch is sent to the list and reviewed there. Change the TEST_LINT variable to run all lint test unless the TEST_LINT variable is overridden. If we hit false positives more often than helping developers to avoid non-portable code (or add less accurate or slow tests later) we could still fall back to exclude them like 81127d74 proposed. Signed-off-by: Jens Lehmann <Jens.Lehmann@web.de> Signed-off-by: Junio C Hamano <gitster@pobox.com>