Limit change-lists report on first/clean builds.

If during a build the workspace has no sync'ed changes from a previous
build (e.g. cstat reports no 'have' entries), then only the last change
'needed' is reported.
Ignore sync messages from p4java.

"file does not exist"  -- when syncing a deleted file revision.
"no file(s) as of that date" -- when resyncing at @0