CXX-648 Add support for targeting OS X El Capitan

Author: acmorrow

SConstruct

@@ -299,7 +299,7 @@ add_option('propagate-shell-environment',
            0, False)
 
 if darwin:
-    osx_version_choices = ['10.6', '10.7', '10.8', '10.9', '10.10']
+    osx_version_choices = ['10.6', '10.7', '10.8', '10.9', '10.10', '10.11']
     add_option("osx-version-min", "minimum OS X version to support", 1, True,
                type = 'choice', default = osx_version_choices[0], choices = osx_version_choices)