Give the changing browser a new session rather than keeping its own

Keeping the session the password was changed from also kept any copy of
its cookie working, and a copied cookie is one of the ways someone else
gets into an account. Every session ends now, and the profile page
signs the browser that changed the password back in with a new one.

From #371.

(cherry picked from commit b01bb7a0a7)

test/models/user_test.rb

@@ -42,15 +42,15 @@ class UserTest < ActiveSupport::TestCase
     end
   end
 
-  test "changing the password outside a request signs out every session" do
-    users(:david).sessions.start!(user_agent: "Other device", ip_address: "127.0.0.1")
+  test "changing the password signs out every session, the current one included" do
+    Current.session = users(:david).sessions.start!(user_agent: "This device", ip_address: "127.0.0.1")
 
     assert_changes -> { users(:david).sessions.count }, to: 0 do
       users(:david).update!(password: "a new secret123456")
     end
   end
 
-  test "changing the password outside a request closes the account's live connections" do
+  test "changing the password closes the account's live connections" do
     remote_connections = mock
     remote_connections.expects(:disconnect).with(reconnect: true)
     ActionCable.server.stubs(:remote_connections).returns(mock.tap { |m| m.expects(:where).with(current_user: users(:david)).returns(remote_connections) })
@@ -58,14 +58,6 @@ class UserTest < ActiveSupport::TestCase
     users(:david).update!(password: "a new secret123456")
   end
 
-  test "changing the password keeps the session it was changed from" do
-    Current.session = users(:david).sessions.start!(user_agent: "This device", ip_address: "127.0.0.1")
-
-    users(:david).update!(password: "a new secret123456")
-
-    assert_equal [ Current.session ], users(:david).sessions.reload
-  end
-
   test "changing other details keeps every session" do
     ActionCable.server.expects(:remote_connections).never