Refactor SOYC artifacts and link process to use disk cache instead of writing individual files into the work directory.

Also makes SyntheticArtifact publically usable and serializable between phases.

Review by: bobv (desk)

git-svn-id: https://google-web-toolkit.googlecode.com/svn/trunk@5445 8db76d5a-ed1c-0410-87a9-c151d255dfc7
13 files changed