Handle crypto db version upgrades

src/errors.js

@@ -1,6 +1,6 @@
 // can't just do InvalidStoreError extends Error
 // because of http://babeljs.io/docs/usage/caveats/#classes
-function InvalidStoreError(reason, value) {
+export function InvalidStoreError(reason, value) {
     const message = `Store is invalid because ${reason}, ` +
         `please stop the client, delete all data and start the client again`;
     const instance = Reflect.construct(Error, [message]);
@@ -22,4 +22,25 @@ InvalidStoreError.prototype = Object.create(Error.prototype, {
 });
 Reflect.setPrototypeOf(InvalidStoreError, Error);
 
-module.exports.InvalidStoreError = InvalidStoreError;
+
+export function InvalidCryptoStoreError(reason) {
+    const message = `Crypto store is invalid because ${reason}, ` +
+        `please stop the client, delete all data and start the client again`;
+    const instance = Reflect.construct(Error, [message]);
+    Reflect.setPrototypeOf(instance, Reflect.getPrototypeOf(this));
+    instance.reason = reason;
+    instance.name = 'InvalidCryptoStoreError';
+    return instance;
+}
+
+InvalidCryptoStoreError.TOO_NEW = "TOO_NEW";
+
+InvalidCryptoStoreError.prototype = Object.create(Error.prototype, {
+  constructor: {
+    value: Error,
+    enumerable: false,
+    writable: true,
+    configurable: true,
+  },
+});
+Reflect.setPrototypeOf(InvalidCryptoStoreError, Error);