Always-on recursive application of all rebar commands causes too many
issues. Recursive application is required for:
1. dealing with dependencies: get-deps, update-deps, and compile of deps
   right after get-deps or update-deps
2. projects with a riak-like apps/ project structure and dev process

The vast majority of projects are not structured like riak. Therefore,
moving forward it's best to (by default) restrict recursive behavior to
dealing with deps. This commit does that and also adds command line and
rebar.config options for controlling or configuring recursion. Also, we
introduce two meta commands: prepare-deps (equivalent to rebar -r
get-deps compile) and refresh-deps (equivalent to rebar -r update-deps
compile). riak-like projects can extend the list of recursive commands
(to include 'eunit' and 'compile') by adding
{recursive_cmds, [eunit, compile]} to rebar.config.

- add overlay_vars=, target_dir=, and tests= with short description

- add missing short and long options
- add tests=, target_dir=, overlay_vars=

- Add 'escriptize' command
- Remove variable 'dump_spec'

For enable to shell-completion in zsh.

This change adds the ability to use alternate urls for downloading
dependencies. To make use of alternate urls run:
rebar get-deps alt_urls=true

Add no_debug_info option.
Remove debug_info=1 option.

Add generate-upgrade and previous_release=.