Prevent continuing disk-space bloat when profiling (with PROFILE_PID_DIR enabled) and autovacuum is on.  Since there will be a steady stream of autovac worker processes exiting and dropping gmon.out files, allowing them to make separate subdirectories results in serious bloat; and it seems unlikely that anyone will care about those profiles anyway.  Limit the damage by forcing all autovac workers to dump in one subdirectory, PGDATA/gprof/avworker/.
Prevent continuing disk-space bloat when profiling (with PROFILE_PID_DIR
enabled) and autovacuum is on.  Since there will be a steady stream of autovac
worker processes exiting and dropping gmon.out files, allowing them to make
separate subdirectories results in serious bloat; and it seems unlikely that
anyone will care about those profiles anyway.  Limit the damage by forcing all
autovac workers to dump in one subdirectory, PGDATA/gprof/avworker/.

Per report from Jrg Beyer and subsequent discussion.

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