This adds a resync.sh script that handles most of the resyncing process:
copying new sources, regenerating help, and staging for commit. I also took
this opportunity to make the process more efficient and consistent by only
selecting the types of files that we care about and ignoring any
autogenerated temporary files that may be in the upstream tree.
Change-Id: Ib0803462684b8ae3b40eec3742944e5bdb28508e
