Merge pull request #2560 from soc/SI-7497-2.9

[backport] SI-7497 Fix scala.util.Properties.isMac
[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.