dedupe git deps

[jonathanong]

right now, i have 16 copies of esprima harmony, and each of those are 6mb large. dedupe doesn't work, maybe because i have like 5 other versions of esprima.

so... if deduping git deps actually works, feel free to close this.

[iarna]

Closing this as fixed in npm/npm#multi-stage. At least, in so far as we're able. For git deps you need to have requested exactly the same thing for them to be considered a duplicate.