Implement environment passthrough (fix #1)
Put makeEnv in seperate function
Merge pull request #8 from scraperwiki/env-passthrough

Implement environment passthrough (fix #1)
Implement notion of different image sources
Enable update signal over localhost HTTP API
Make Run/Build take the UpdateEvent
Add OutputStream and BuildComplete to UpdateEvent
Send build result over HTTP request
Implement BuildTarballContent
Flush every line during build
Ignore /iptables
Support zip uploads