replaced prototyped pseudo-private functions with file-scoped functions in the module core

Signed-off-by: Ayudh Das <ayudh.d@gmail.com>
removed unnecessary comments and fixed the failing test case

Signed-off-by: Ayudh Das <ayudh.d@gmail.com>
Added cull to DrawCommand
Merge pull request #733 from AnalyticalGraphicsInc/cull

Terrain performance improvement
Merge pull request #727 from ayudhDas/issue-705

replaced prototyped pseudo-private functions with file-scoped functions ...
Add ayudhDas, his first pull request was #727
Merge branch 'master' of github.com:AnalyticalGraphicsInc/cesium into examples