armh: cope with non-signed repository hashes

The '[alt]' signature reference in the stock package
doesn't fit current reality as the hash files for
Sisyphus/armh are *not* cryptographically signed.

This commit should be reverted when these are.

features.in/armh/rootfs/image-scripts.d/91-unsigned-repo

@@ -0,0 +1,7 @@
+#!/bin/sh
+# Sisyphus/armh is not being signed as of June, 2013
+
+repo_source='/etc/apt/sources.list.d/alt.list'
+[ -s "$repo_source" ] || exit 0
+
+sed -i 's, \[alt\],,' "$repo_source" ||: