deps: add new clause of format_source function

Function format_source in rebar_deps.erl will fail on sources
like {rsync, Path} or {hg, URL} in rebar.config.
Add new function clause to match such source types.
Merge branch 'fix_format_source' of https://github.com/irpab/rebar into irpab-fix_format_source

Conflicts:
	THANKS
Merge branch 'irpab-fix_format_source'