Demangle an example file in the tests correctly.

As was, this left each line with a leading space, and automake then went on to
complain that it hadn't seen a valid @setfilename line.

diff -x config.log -x config.status -ru tmp/automake-1.12.3/t/distcheck-override-infodir.sh work/automake-1.12.3/t/distcheck-override-infodir.sh
--- tmp/automake-1.12.3/t/distcheck-override-infodir.sh	2012-08-13 17:40:13.000000000 +0100
+++ work/automake-1.12.3/t/distcheck-override-infodir.sh	2012-08-16 15:11:32.391000014 +0100
@@ -39,7 +39,7 @@
 END
 
 # Protect with leading " # " to avoid spurious maintainer-check failures.
-sed 's/^ #//' > main.texi << 'END'
+sed 's/^ # //' > main.texi << 'END'
  # \input texinfo
  # @setfilename main.info
  # @settitle main