OSIdentifier no longer properly identifies OS because mrj.version returns null

[martinrleon]

Probably something Oracle changed. The check for mrj.version returns null on OS X.

Fixing this along with the last 2 issues I submitted enables me to run the test app I wrote for Isssue #2

You may want to change the code as follows as there doesn't appear to be a way to distinguish the OS vs hardware platform and some FEST code relies on isOSX and some on isMacintosh:

isOSX = osName.contains("os x");
isMacintosh = isOSX;

https://github.com/alexruiz/fest-swing-1.x/blob/master/fest-swing/src/main/java/org/fest/swing/util/OSIdentifier.java#L56