Fix deadlock in .pro file evaluation.

We used to indicate that the cache for a file is up to date by having a
Entry with ent->locker == 0. But we first wake up all threads and only
after all the threads who waited for that parse to complete we set
ent->locker to zero. Thus a different thread could get the impression
that it needs to wait for the parse thread, yet get no wake up.

We need a different flag to indicate that we are actually already done
parsing and the cache can simply be used instead of waiting for a wake
up.

Reviewed-By: ossi