Small updates to kernel 4.
Small updates to kernel 4.

- Added comments regarding the barriers and use of replicated level
  sets

- Implemented a small optimization that avoided the reduction over
  Active_Remaining for the first iteration

- Added other comment regarding possible improvements




git-svn-id: 88467cb1fb04b8a755be7e1ee1026be4190196ef@19046 3a8e244f-b0f2-452b-bcba-4c88e055c3ca

CoryMcCartan/chapel,CoryMcCartan/chapel,chizarlicious/chapel,sungeunchoi/chapel,CoryMcCartan/chapel,chizarlicious/chapel,chizarlicious/chapel,hildeth/chapel,sungeunchoi/chapel,hildeth/chapel,sungeunchoi/chapel,sungeunchoi/chapel,sungeunchoi/chapel,chizarlicious/chapel,hildeth/chapel,hildeth/chapel,sungeunchoi/chapel,CoryMcCartan/chapel,sungeunchoi/chapel,chizarlicious/chapel,hildeth/chapel,CoryMcCartan/chapel,CoryMcCartan/chapel,CoryMcCartan/chapel,chizarlicious/chapel,hildeth/chapel,sungeunchoi/chapel,hildeth/chapel,chizarlicious/chapel