[backport] SI-7497 Use `osName startsWith "Mac OS X"` ...

... instead of `osName contains "OS X"`

See http://mail.openjdk.java.net/pipermail/macosx-port-dev/2012-November/005148.html
for the reason why we don't follow developer.apple.com/library/mac/#technotes/tn2002/tn2110.