rebar_config:is_verbose/0: fix variable name
rebar_log: use defines for log level numbers
Change default log level to 'warn' and introduce -q/--quiet
Write ERROR messages to standard_error device
Fix is_verbose/1 helper function
Implement meta command 'prepare-deps'

'rebar prepare-deps' is equivalent to 'rebar -r get-deps compile'.
Implement meta command 'refresh-deps'

'rebar refresh-deps' is equivalent to 'rebar -r update-deps compile'.
Merge remote-tracking branch 'tuncer/logging' into heroku_new
Merge remote-tracking branch 'tuncer/auto-recursion' into heroku_new

Conflicts:
	src/rebar_config.erl