Mock objects are no longer used as app hook targets in unit tests. (refs #12)

Because ARC is incompatible to weak references to NSProxy-derived objects
in iOS 5 (http://stackoverflow.com/questions/9104544/how-can-i-get-ocmock-under-arc-to-stop-nilling-an-nsproxy-subclass-set-using-a-w).

We're still able to use mocks to verify that the hooks are called by partially mocking
real targets.
Make sure not to reference UIAccessibilityTraitHeader on iOS 5. (refs #12)

It's not available until 6.
Turn off auto-layout on two more XIBs. (refs #12)

These XIBs can't be unarchived on iOS 5, also we're not using
constraints anyway.
Attribute the proper bugs to UIAElement.isVisible on iOS 5. (refs #12)

It doesn't always return true for accessibility elements in table view cells,
as it does in iOS 6; but it does fail to update for a newly-appeared
table view cell child element.
Avoid using iOS 6-specific UITableView APIs in Subliminal's integration tests. (refs #12)
Increase the startup timeout. (refs #12)

With the simulator running iOS 5, I'm seeing Instruments take a few seconds
to actually start running SLTerminal.js. Strangely, this delay doesn't take place
on the first run of Instruments--only if you make changes to the tests and then
relaunch Instruments.

Anyway, we now give Instruments a few more seconds, on both platforms,
before we decide that SLTerminal/SLTerminal.js have failed and abort the tests.
Execute the character-wise typing loop entirely within JavaScript. (refs #12)

For improved performance, both in terms of not needing to create substrings
and not needing to send multiple commands to the terminal.
Move the SLTextField test cases' text fields up above the keyboard.

This is just an aesthetic tweak.
`rake test:unit` now executes Subliminal's unit tests against both iOS 5.1 and 6.1. (refs #12)
`set_simulator_device` is now a shell script.

For increased reliability.
Use string comparisons rather than boolean comparisons where appropriate in `subliminal-test`.
Factor `subliminal-test` build command into function.

To avoid recreating the command in the multiple places it is used.
`subliminal-test` now optionally tests against a particular simulator SDK. (refs #12)

The instruments command-line tool will not run tests against any SDK other than
the latest (http://stackoverflow.com/questions/12836129/launch-a-specific-hardware-version-of-ios-simulator-using-instruments-command-li),
so `subliminal-test` now runs Simulator-targeted tests using the Instruments GUI.

`subliminal-test` dynamically generates configuration-specific trace templates
to avoid having to GUI-script the configuration of Instruments; `run_template.scpt`
is used only to toggle recording and to save the trace document when recording
has concluded.
Subliminal now runs its integration tests on both iOS 5.1 and 6.1. (resolves #12)