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

t/test-lib.sh

@@ -386,6 +386,7 @@ unset VISUAL EMAIL LANGUAGE COLUMNS $("$PERL_PATH" -e '
 	my @env = keys %ENV;
 	my $ok = join("|", qw(
 		TRACE
+		TR2_
 		DEBUG
 		TEST
 		.*_TEST