compile for iOS 5.1 since it is the latest stable version and backward compatible to 5.0

iOS 4 is used by less than 10 per cent of the installed base, so we don't care for now

extras/package/ios/build.sh

@@ -3,7 +3,7 @@ set -e
 
 PLATFORM=OS
 VERBOSE=no
-SDK_VERSION=5.0
+SDK_VERSION=5.1
 SDK_MIN=5.0
 
 usage()