environs: turn environment configuration into a concrete type

environs/ec2/config.go

 package ec2
 
 import (
         "fmt"
         "launchpad.net/goamz/aws"
         "launchpad.net/juju-core/environs/config"
         "launchpad.net/juju-core/schema"
 )
 
 // providerConfig is a placeholder for any config information
@@ skipping 16 matching lines @@
                 "public-bucket":        schema.String(),
         }, []string{
                 "access-key",
                 "secret-key",
                 "region",
                 "public-bucket",
         },
 )
 
 func newConfig(config *config.Config) (*providerConfig, error) {
-        v, err := configChecker.Coerce(config.TypeMap(), nil)
+        v, err := configChecker.Coerce(config.UnknownAttrs(), nil)
         if err != nil {
                 return nil, err
         }
         m := v.(schema.MapType)
         c := &providerConfig{Config: config}
         c.bucket = m["control-bucket"].(string)
         c.publicBucket = maybeString(m["public-bucket"], "")
         c.auth.AccessKey = maybeString(m["access-key"], "")
         c.auth.SecretKey = maybeString(m["secret-key"], "")
         if c.auth.AccessKey == "" || c.auth.SecretKey == "" {
@@ skipping 16 matching lines @@
         c.region = regionName
         return c, nil
 }
 
 func maybeString(x interface{}, dflt string) string {
         if x == nil {
                 return dflt
         }
         return x.(string)
 }