Remove vestiges of 10.5 support.

Spy driver no longer needs:
- special copied 10.5 SDK
- to use LDFLAGS to pick which framework to link against

Apps now use 10.6 as minimum system version for all arches.
We can now use GCD without checking for its existence.
Fix potential leaks in error conditions
Fix unsafe calls to objc_msgSend
Merge branch 'master' of https://github.com/DouglasHeriot/MIDIApps into DouglasHeriot-master
Post-merge cleanup:

- CHECK_FOR_GCD has been removed
- check for null before calling dispatch_release
Post merge cleanup:

- Mark source file as UTF-8
- dispatch_once to set up static array
ignore Xcode 5 *.xccheckout
More changes to placate Xcode 5
Use @rpath for framework install paths.
Fix analyzer warning
Avoid using @property and synthesize for a dispatch queue.

It's causing issues when including this header in ARC code.
Also will confuse things depending on whether the compiler
knows how to ARCify dispatch queues (which changed at
some point). Easier to avoid the whole issue.