Get Travis CI tests green / Remove Rcov from Rakefile

This was originally intended to be a much narrower PR, but I discovered that the Travis CI tests were failing across the board.  So in addition to the original intent (removing rcov from the Rakefile), I made a number of changes to get the tests green.  These were:

1. Pull scrypt out of the gemspec and make it optional, as it is only supported on MRI platforms.  Update the Appraisals and Gemfile to reflect this.  Tests for this feature now only run on MRI platforms
2. Restrict scrypt to a version that is compatible with Ruby 1.8.7
3. Restrict timecop to a version that is compatible with Ruby 1.8.7, ree, and JRuby
4. Pull sqlite3 out of the gemspec, as this gem is not compatible with JRuby.  Use it for all non JRuby platforms.  Use the appropriate JDBC Sqlite gem for Rails 3 and Rails 4 when using JRuby.
5. Update tests so that they don't depend on Test::Unit::TestCase, which no longer exists in Rails 4.  Include directly against ActiveSupport::TestCase
6. Remove the gemfiles/*.lock files from the repo, as these need to be built dynamically by Travis CI
7. Use a different approach to set the updated_at attribute on models in tests.  The previously used version was setting the wrong values in Rails 4
8. Make the tests aware of the ActiveModel version so that they can check the correct key in the errors hash for password-related errors.  Rails 4 changed where some errors are stored

The entire test matrix is now green, and all tests run on the platforms that support them.  You can find a Travis CI run here - https://travis-ci.org/petergoldstein/authlogic/builds/10251971