Support custom feeds when in classic mode

When in classic mode (ie. havent added any ripples.dependencies.config), i cannot add package from a custom feed. Dunno if i'm doing "ripple" totally wrong. but my flow was like so:
1. New solution
2. ripple init
3. Add custom feed to ripple.config
4. ripple install {some internal package} <-- didn't read the feeds from ripple.config

quite new to ripple so dunno if its a feature or a bug