Ensure compatible arch before launching on device

[jmoody]

Motivation

Before launching an app on iOS, ensure that the architecture of the CFBundleExecutable is compatible with the target device. #75

If the binary and the simulator target are not compatible, an error will raised before launch.

RunLoop::IncompatibleArchitecture: Binary at:
/Users/moody/git/run-loop/spec/resources/lipo/x86_64/chou.app/chou
does not contain a compatible architecture for target device.
Expected 'i386' but found ["x86_64"].

Todo

• I think we need some error handling in the RunLoop::Lipo class. UPDATE: Let's forgo the error handling until becomes an issue.

Missing behaviors

There are two compatibility checks that are missing: is the binary compatible with a physical device and is the binary compatible with the form factor.

Checks against physical devices will require integrating a tool like ideviceinfo because we cannot find information about a device's instruction set using Xcode tools; all we have is the UDID.

We can check that the binary is compatibility with the form factor (e.g. Is this an iPad only app?) by inspecting the Info.plist. This behavior belongs in another PR.

Testing

$ be rake spec/integration/simulator_compatibility_spec.rb
Simulator/Binary Compatibility Check
  raises an error if libraries are not compatible
    targeting i386 simulator with binary that contains only a x86_64 slice
    target only has arm slices
  can launch if library is FAT
    targeting x86_64 simulator with binary that contains only a i386 slice
    can launch if libraries are compatible

@krukow @svevang