Remove plugins before copying them again.

This way plugins can rename/delete files w/o having old files lying around.
Only delete core plugins.
Added man page plugin command warning

As of now, the man page does not update when plugins are installed.
Updated man page date

I forgot to change it. I even left myself a reminder!
Use PLUGIN_PATH in dokku default case.
move post-deploy hook

Write $DOKKU_ROOT/$APP/URL before post-deploy hook.
Make help output more consistent
Actually suppress the output from the git commands
Use -qq flag on apt-get to quiet installations of packages
Silence curl stderr progress output
Ensure curl is installed before using command
Fix issue where certain hosts will not have add-apt-repository installed due to missing packages
Simplify the vagrant workflow

- Moved from wget to cloning the repository
- Add acl-add command to Make
- Modify the docs to use the new methodology
Add a passthru make target for running dokku commands within the vagrant vm
Change targets to vagrant-*
Merge pull request #708 from progrium/576-fix-vagrant

576 fix vagrant
Merge pull request #698 from tombell/clean-up-help

Make `help` command output more consistent
Explicitly install man-db

Dokku requires mandb, but the man-db package is not part of the
minimal Ubuntu base - so install it.
Merge branch 'install_man-db'
Restart app only if config changed