HEADS-UP: Bumping minimum OS X version to build FX 9 to OS X 10.9

[Kevin Rushforth]

We currently build FX 9 on Mac OS X 10.9.5 and run on 10.9.5 or later. 
As part of an ongoing effort to cleanup old, unused code that is only 
there to support older OS versions, we filed the following two issues:

https://bugs.openjdk.java.net/browse/JDK-8145602
https://bugs.openjdk.java.net/browse/JDK-8145604

The impact of this cleanup is that FX 9 will no longer build with OS X 
10.8 or earlier. You will need at least OS X 10.9.5 and XCode 5.1.1 in 
order to build FX 9.

Note that the minimum version of Mac OS X that will be supported in JDK 
9 is 10.10, although we intend to keep FX buildable and runnable on OS X 
10.9.5 for the foreseeable future.

-- Kevin