CURL: added global curl initialization to the Registry ctor since it's not thread safe
Merge branch 'master' of github.com:gwaldron/osgearth
CURL: moved the global_init into a static HTTPClient function instead
Threading issue with MacOSX 10.8

Hi
This should solve #298 on MacOSX 10.8. I didn't tested 10.7/6 or iOS.
BYO terrain engine works with shadergen; shadergen state sharing integrated
Added byo example
Merge pull request #300 from remoe/patch-2

Threading issue with MacOSX 10.8. Should solve #298
Using the scene technique in osgearth_terrain profile so it performs better than map.
Merge remote-tracking branch 'refs/remotes/upstream/master' into topic-terra