pgsql: Extend yesterday's patch so that the bgwriter is also told to

Log Message:
-----------
Extend yesterday's patch so that the bgwriter is also told to forget
pending fsyncs during DROP DATABASE. Obviously necessary in hindsight :-(

Modified Files:
--------------
pgsql/src/backend/commands:
dbcommands.c (r1.189 -> r1.190)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/src/backend/commands/dbcommands.c.diff?r1=1.189&r2=1.190)
pgsql/src/backend/postmaster:
bgwriter.c (r1.35 -> r1.36)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/src/backend/postmaster/bgwriter.c.diff?r1=1.35&r2=1.36)
pgsql/src/backend/storage/smgr:
md.c (r1.126 -> r1.127)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/src/backend/storage/smgr/md.c.diff?r1=1.126&r2=1.127)
pgsql/src/include/storage:
smgr.h (r1.57 -> r1.58)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/src/include/storage/smgr.h.diff?r1=1.57&r2=1.58)