[DEV-458] Prefer not to use the same server when retrying a request.
Add NULL check to load_balance_by_weight()
[DEV-482] Try different TM processes if one of them fails
refactor retry ranges check to separate function
[DEV-482] Implement Aaron's suggestions
Merge pull request #26 from flowroute/DEV-482

[Dev 482] Try another tm process if sendto() fails