xautoload 7.x-5.0-beta1

First release of the 7.x-5.x branch.
Changes to 7.x-4.x as in https://drupal.org/node/2271469

• New default mapping: {"psr-4": {"Drupal\\$module_name\\": "$module_dir/src/"}} for each enabled module.
• New mechanics to guarantee that hook_xautoload() and hook_libraries_info() are executed on request start, and when new modules are enabled (incl xautoload).
• New mechanics to guarantee that default module namespaces are registered damn early on module install.
  Yes, you can now use your classes directly from hook_enable(), hook_install() and hook_schema()! Awesome, or not?
• Architecture now cleaner (I hope)
• A lot of stuff covered by phpunit, with a VirtualDrupal environment, simulating bootstrap and module enabling in different situations. These tests execute in seconds!