From Bob Kuehne, build fix for OSX 10.7 SDK.
From Stephan Huber, fixed build for OSX 10.6 and earlier
From Ulrich Hertlein, Added some error checks and memory cleanup.
src/osgViewer/DarwinUtils.mm: OSG_WARN -> OSG_NOTIFY(osg::WARN)

- The `OSG_WARN`s were introduced by 26c313daf47501c9aed2dbcf3a112b3caee6cedf (cherry picked from bac863c339a11516e0b1f53e4355b45062114b6e)
- `OSG_WARN` was introduced to osg in b7b0a0062869e2dc89b9a2fae40c0390f7fa5c93 to replace `OSG_NOTIFY(osg::WARN)`, but this is not part of the 2.8.* releases
Merge pull request #3 from casallas/new-wrappers-macfix

Fix build on Mac OS X > 10.6