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)
Disable all testing against the 5.1 SDK when running on Travis. (refs #18)

They do not yet have that SDK installed: https://github.com/travis-ci/travis-ci/issues/1157.