Ookay, last reshuffle.

 * openstack.NewClient() normalizes the identity endpoint with a trailing slash, and sets base and endpoint.
 * utils.ChooseVersion() checks suffixes first to short-circuit actual version calls.
 * gophercloud.ProviderClient distinguishes between the root of all identity services (IdentityBase)
   and the endpoint of the requested auth service (IdentityEndpoint).
diff --git a/openstack/utils/choose_version_test.go b/openstack/utils/choose_version_test.go
index b724ee8..9552696 100644
--- a/openstack/utils/choose_version_test.go
+++ b/openstack/utils/choose_version_test.go
@@ -40,10 +40,10 @@
 	defer testhelper.TeardownHTTP()
 	setupVersionHandler()
 
-	v2 := &Version{ID: "v2.0", Priority: 2}
-	v3 := &Version{ID: "v3.0", Priority: 3}
+	v2 := &Version{ID: "v2.0", Priority: 2, Suffix: "blarg"}
+	v3 := &Version{ID: "v3.0", Priority: 3, Suffix: "hargl"}
 
-	v, endpoint, err := ChooseVersion(testhelper.Endpoint(), []*Version{v2, v3})
+	v, endpoint, err := ChooseVersion(testhelper.Endpoint(), "", []*Version{v2, v3})
 
 	if err != nil {
 		t.Fatalf("Unexpected error from ChooseVersion: %v", err)
@@ -64,10 +64,32 @@
 	defer testhelper.TeardownHTTP()
 	setupVersionHandler()
 
-	v2 := &Version{ID: "v2.0", Priority: 2}
-	v3 := &Version{ID: "v3.0", Priority: 3}
+	v2 := &Version{ID: "v2.0", Priority: 2, Suffix: "nope"}
+	v3 := &Version{ID: "v3.0", Priority: 3, Suffix: "northis"}
 
-	v, endpoint, err := ChooseVersion(testhelper.Endpoint()+"v2.0/", []*Version{v2, v3})
+	v, endpoint, err := ChooseVersion(testhelper.Endpoint(), testhelper.Endpoint()+"v2.0/", []*Version{v2, v3})
+	if err != nil {
+		t.Fatalf("Unexpected error from ChooseVersion: %v", err)
+	}
+
+	if v != v2 {
+		t.Errorf("Expected %#v to win, but %#v did instead", v2, v)
+	}
+
+	expected := testhelper.Endpoint() + "v2.0/"
+	if endpoint != expected {
+		t.Errorf("Expected endpoint [%s], but was [%s] instead", expected, endpoint)
+	}
+}
+
+func TestChooseVersionFromSuffix(t *testing.T) {
+	testhelper.SetupHTTP()
+	defer testhelper.TeardownHTTP()
+
+	v2 := &Version{ID: "v2.0", Priority: 2, Suffix: "/v2.0/"}
+	v3 := &Version{ID: "v3.0", Priority: 3, Suffix: "/v3.0/"}
+
+	v, endpoint, err := ChooseVersion(testhelper.Endpoint(), testhelper.Endpoint()+"v2.0/", []*Version{v2, v3})
 	if err != nil {
 		t.Fatalf("Unexpected error from ChooseVersion: %v", err)
 	}