Make CHPL_NETWORK_ATOMICS overridable
Make CHPL_NETWORK_ATOMICS overridable

Forgot to put in the case where the user sets CHPL_NETWORK_ATOMICS
explicitly (which is convenient for performance comparisons).



git-svn-id: 88467cb1fb04b8a755be7e1ee1026be4190196ef@20318 3a8e244f-b0f2-452b-bcba-4c88e055c3ca

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