Tweak postgresql.conf.sample's comments on listen_addresess.

This makes it slightly more clear that '*' is not part of the default
value, in case that wasn't obvious.

As requested by Dougal Sutherland.

src/backend/utils/misc/postgresql.conf.sample

@@ -58,7 +58,7 @@
 
 #listen_addresses = 'localhost'		# what IP address(es) to listen on;
 					# comma-separated list of addresses;
-					# defaults to 'localhost', '*' = all
+					# defaults to 'localhost'; use '*' for all
 					# (change requires restart)
 #port = 5432				# (change requires restart)
 #max_connections = 100			# (change requires restart)