tests/test-diff-reverse.out

alias: do not crash when aliased command has no usage help text

adding a
diff -r 2855cdcfcbb7 -r 8e1805a3cf6e a
--- a/a	Thu Jan 01 00:00:00 1970 +0000
+++ b/a	Thu Jan 01 00:00:00 1970 +0000
@@ -1,3 +1,3 @@
-d
-e
-f
+a
+b
+c
diff -r 2855cdcfcbb7 a
--- a/a
+++ b/a
@@ -1,5 +1,3 @@
 d
 e
 f
-g
-h