t6000lib: tr portability fix

Some versions of tr complain if the number of characters in
both sets isn't the same. So here we must manually expand
the dashes in set2.

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

t/t6000lib.sh

@@ -97,7 +97,10 @@ check_output()
 # from front and back.
 name_from_description()
 {
-        tr "'" '-' | tr '~`!@#$%^&*()_+={}[]|\;:"<>,/? ' '-' | tr -s '-' | tr '[A-Z]' '[a-z]' | sed "s/^-*//;s/-*\$//"
+        tr "'" '-' |
+		tr '~`!@#$%^&*()_+={}[]|\;:"<>,/? ' \
+		   '------------------------------' |
+		tr -s '-' | tr '[A-Z]' '[a-z]' | sed "s/^-*//;s/-*\$//"
 }