Export more test-related variables when running external tests

Add exporting TEST_DIRECTORY and TRASH_DIRECTORY to test_external, for
external tests to be able to find test script (and git sources), and
to find trash directory (usually with test repository in it).

Add also exporting GIT_TEST_LONG, so that external test can skip
time-intensive tests unless test is invoked with `--long' option.

Signed-off-by: Jakub Narebski <jnareb@gmail.com>
Acked-by: Petr Baudis <pasky@suse.cz>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

t/test-lib.sh

@@ -459,6 +459,9 @@ test_external () {
 		# Announce the script to reduce confusion about the
 		# test output that follows.
 		say_color "" " run $test_count: $descr ($*)"
+		# Export TEST_DIRECTORY, TRASH_DIRECTORY and GIT_TEST_LONG
+		# to be able to use them in script
+		export TEST_DIRECTORY TRASH_DIRECTORY GIT_TEST_LONG
 		# Run command; redirect its stderr to &4 as in
 		# test_run_, but keep its stdout on our stdout even in
 		# non-verbose mode.