Set config.global_id.verifier to nil if #message_verifier raises
Squashed commit of the following:

commit d38db7346954fc342edbea7b18ddc6cce3088fe4
Author: Dan Olson <olson_dan@yahoo.com>
Date:   Mon Aug 18 22:07:10 2014 -0500

    Remove unused variable in test and update assertion
Ensure SignedGlobalID.verifier is reset properly
Rescue ArgumentError specifically
Allow a verifier option to be passed to SignedGlobalID. Raise in SignedGlobalID.parse when verifier is nil as well
Merge pull request #19 from DanOlson/no-verifier-on-init

Set config.global_id.verifier to nil if #message_verifier raises
Signed Global IDs accept a :verifier and default to SignedGlobalID.verifier
[Fix] Use ActiveSupport::TestCase instead of ActiveModel::TestCase
Merge pull request #22 from seuros/master

[Fix] Use ActiveSupport::TestCase instead of ActiveModel::TestCase
Remove Gemfile.lock
Ignore Gemfile.lock as well
fix typo in README.md
Merge pull request #26 from damien-roche/master

fix typo in README.md
[Fix] App name cannot contain an underscore , closes #23
Merge pull request #25 from seuros/master

[Fix] App name cannot contain an underscore , closes #23
Apps can hook in their own locator.

Move only resctriction to locator.

Memoize default locator. Privatize class methods properly.

Make app name validating public.

Use app validation on GlobalID.

Normalize app names when reading or setting locators.
Merge pull request #15 from kaspth/app-locater

Apps can hook in their own locator.
[Refactoring] Use AS dasherize instead of gsub
signing with purpose via :for option

override == in SignedGlobalID to consider purpose

change serializer to JSON and clear the tests
Merge pull request #20 from tony612/signing-with-purpose

signing with purpose via :for option