upgrade submodule fuego-on-ios to latest version that allows iOS 7.1 builds
upgrade project to iOS 7.1 / Xcode 5.1.1 / clang 3.4

change details:
- upgrade submodule fuego-on-ios to latest version that allows iOS 7.1
  builds. as a "side-effect", this version of fuego-on-ios also builds
  with architectures arm64 and x86_64, drops the armv6 build, and raises
  the deployment target from 5.0 to 7.0
- the project now uses base SDK 7.1 and deployment target 7.0
- the ARCHS build setting is now set to $(ARCHS_STANDARD_32_BIT);
  although Boost and Fuego now support 64-bit builds (see above), other
  3rdparty software (CrashReporter, MBProgessHUD) is not yet there
- explicitly link against libstdc++; apparently the default in Xcode
  5.1.1 (or is it clang 3.4?) has changed to link against libc++;
  unfortunately we can't go with the new default yet because Boost does
  not yet support linking against libc++
fix warnings about things that have been deprecated in iOS 7.0

these warnings did not surface before because up until recently we were
still using iOS 6.1 as deployment target
automatic changes made by Xcode 5.1.1 to fix code signing / provisioning issues
set "build active architecture only" to true for Debug configuration

makes the debug build faster because unnecessary architectures are not
build.

the change to the project settings was automatically performed by Xcode.
it appears that as a side-effect Xcode sets the LastUpgradeVersion and
LastUpgradeCheck properties in various project files.