Gyu-Ho Lee e0ddded077 auth: simplify merging range perm
No need of separate function to filter duplicates.
Just merge ranges in-place

```
go test -v -run=xxx -bench=BenchmarkMergeOld -benchmem
BenchmarkMergeOld-8   	  100000	     13524 ns/op	    1104 B/op	       8 allocs/op

go test -v -run=xxx -bench=BenchmarkMergeNew -benchmem
BenchmarkMergeNew-8   	  100000	     13432 ns/op	     936 B/op	       3 allocs/op
```

Not much performance boost, but less memory allocation
and simpler
2017-02-13 16:37:43 -08:00
..
2016-11-10 12:02:00 -08:00