Merge branch 'ab/test-lib-pass-trace2-env'

Allow tracing of Git executable while running the testsuite.

* ab/test-lib-pass-trace2-env:
  test-lib: whitelist GIT_TR2_* in the environment
diff --git a/t/test-lib.sh b/t/test-lib.sh
index 38b1570..d18387c 100644
--- a/t/test-lib.sh
+++ b/t/test-lib.sh
@@ -386,6 +386,7 @@
 	my @env = keys %ENV;
 	my $ok = join("|", qw(
 		TRACE
+		TR2_
 		DEBUG
 		TEST
 		.*_TEST