[vpython] Fix flag parsing bug with "--".

vpython/application/flag.go

 // Copyright 2017 The LUCI Authors. All rights reserved.
 // Use of this source code is governed under the Apache License, Version 2.0
 // that can be found in the LICENSE file.
 
 package application
 
 import (
         "flag"
         "strings"
 )
@@ skipping 15 matching lines @@
                 return
         case len(args[0]) == 0 || args[0][0] != '-':
                 // If our first argument isn't a flag, then everything belongs to
                 // "remainder", no processing necessary.
                 remainder = args
                 return
         }
 
         // Scan "args" for a "--" divider. We only process candidates to the left of
         // the divider.
         candidates := args

[qyearsley, 2017/06/15 20:12:54]

One thing that isn't very clear to me when reading this file is, what does
candidates refer to here? The candidates are a subset of the args, but what are
they candidates for? Candidates for being vpython args? Also, what is fsArgs?

         for i, arg := range args {
                 if arg == "--" {
                         candidates = args[:i]
                         break
                 }
         }
         if len(candidates) == 0 {
                 remainder = args
                 return
         }
@@ skipping 41 matching lines @@
                 }
                 if flagIsBool || single {
                         return 1
                 }
                 return 2
         }
 
         for i := 0; i < len(candidates); {
                 consume := processOne(candidates[i:])
                 if consume == 0 {
-                        fsArgs, remainder = args[:i], candidates[i:]
+                        fsArgs, remainder = args[:i], args[i:]
                         return
                 }
                 i += consume
         }
 
         // Got to the end with no non-"fs" flags, so everything goes to fsArgs.
         fsArgs, remainder = candidates, args[len(candidates):]
         return
 }