t5000: extract nongit function to test-lib-functions.sh

This function abstracts the idea of running a command
outside of any repository (which is slightly awkward to do
because even if you make a non-repo directory, git may keep
walking up outside of the trash directory). There are
several scripts that use the same technique, so let's make
the function available for everyone.

Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

t/t5000-tar-tree.sh

@@ -94,20 +94,6 @@ check_tar() {
 	'
 }
 
-# run "$@" inside a non-git directory
-nongit () {
-	test -d non-repo ||
-	mkdir non-repo ||
-	return 1
-
-	(
-		GIT_CEILING_DIRECTORIES=$(pwd) &&
-		export GIT_CEILING_DIRECTORIES &&
-		cd non-repo &&
-		"$@"
-	)
-}
-
 test_expect_success \
     'populate workdir' \
     'mkdir a &&

t/test-lib-functions.sh

@@ -994,3 +994,17 @@ test_copy_bytes () {
 		}
 	' - "$1"
 }
+
+# run "$@" inside a non-git directory
+nongit () {
+	test -d non-repo ||
+	mkdir non-repo ||
+	return 1
+
+	(
+		GIT_CEILING_DIRECTORIES=$(pwd) &&
+		export GIT_CEILING_DIRECTORIES &&
+		cd non-repo &&
+		"$@"
+	)
+}