pgsql: Prevent continuing disk-space bloat when profiling (with

Log Message:
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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 J�rg Beyer and subsequent discussion.

Modified Files:
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pgsql/src/backend/storage/ipc:
ipc.c (r1.97 -> r1.98)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/src/backend/storage/ipc/ipc.c?r1=1.97&r2=1.98)