Change VersioncontrolRepository::update_method to be a simple flag for cron

I think this patch does it:

• Changes {versioncontrol_repositories} update_method field to be named cron and be a simple flag.
• Removes VersioncontrolBackend::update_methods data member.
• Renames VersioncontrolRepository update_method data member to cron.
• Removes versioncontrol_handler_field_repository_update_method views field handler.
• Updates views implementation, views default view for repository listing and tests to follow the schema changes.
• Implements hook_cron() to process syncronizations of repositories marked to do it on cron.

Let's see what bot thinks.

PS: I have two commits locally for this patch to differentiate views re-export change.

Last patch added to 7.x-1.x

I reworked the change for 6.x-2.x as in the patch an added it.

Copying conflict section from commit message:

    Conflicts:
      Some changes needed to be done manually: change hook_update_N() to use
      D6 api and change hook_views_handlers() which exists on D6 but not on
      D7.
      includes/views/versioncontrol.views_default.inc
        This needed to be changed/re-exported manually, since D7 ad D6 views
        exports are different.
      versioncontrol.admin.inc
        Minor string conflict.
      versioncontrol.info
        Minor: On D6 handlers are not declared here.
      versioncontrol.module
        Minor Implemented/Implements docblock conflict.