The new process pool allows adding jobs after testing has been started. It will also allow to restructure building the job queue (in a follow up CL), so that testing can start instantly while the queue is being built.

Also attempts to clean up the keyboard-interrupt logic. Idea: Only catch keyboard interrupt once per process at the outermost level. Use proper "finally" clauses to clean up everywhere where a keyboard interrupt might occur. Never turn named exceptions into none-exceptions using anonymous "raise".

TEST=python -m unittest pool_unittest
R=jkummerow@chromium.org

Review URL: https://codereview.chromium.org/275093002

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@21310 ce2b1a6d-e550-0410-aec6-3dcde31c8c00