getpid/pid cleanup

src/backend/bootstrap/bootstrap.c

src/backend/commands/async.c

src/backend/commands/user.c

src/backend/executor/nodeHash.c

src/backend/libpq/pqcomm.c

src/backend/postmaster/postmaster.c

src/backend/storage/buffer/bufmgr.c

src/backend/storage/lmgr/lock.c

src/backend/storage/lmgr/proc.c

src/backend/tcop/postgres.c

src/backend/tcop/utility.c

src/backend/utils/error/elog.c

src/backend/utils/init/globals.c

src/backend/utils/sort/psort.c

src/include/miscadmin.h

src/include/storage/proc.h