Merge pull request #24 from hnousiainen/master

execute shell worker modifications
frontend: use webob for request/response decoding/encoding
build: new pylint configuration
pylint cleanups
git-checkout/doc: use full git references
frontend: move argument validation into request handlers
frontend: github webhook trigger
execute-shell: dirty fix to deal with UTF-8 console output
frontend: rename distlocks to sync
sync: introduce phony lock for dev/test
frontend: maintain task state in zookeeper
build_control: fix error handling for unknown worker type