Fix autogen.sh to be more portable and to fail when autoreconf fails

autogen.sh

@@ -2,5 +2,6 @@
 # to really generate all files you need to run "make distcheck" in a
 # object tree, but this will do if you have all parts of the required
 # tool-chain installed
+set -e
 autoreconf -f -i || { echo "autoreconf failed: $?"; exit 1; }
-find . \( -name '*-private.h' -o -name '*-protos.h' \) -delete
+find . \( -name '*-private.h' -o -name '*-protos.h' \) | xargs rm