Enable vmiodirenable by default. Remove incorrect comment from sysctl.conf.

MFC after:	1 week

etc/sysctl.conf

@@ -4,9 +4,3 @@
 #  ``sysctl'' to adjust kernel values.  ``man 5 sysctl.conf'' for details.
 #
 
-#vfs.vmiodirenable=0	# Set to 1 to enable the use of the VM subsystem to
-			# back UFS directory memory requirements. Because of
-			# the amount of wasted memory this causes it's not
-			# advised for machines with less than 64MB of RAM, but
-			# on machines with more than 64MB it can provide a
-			# substantial benefit related to directory caching.

sys/kern/vfs_bio.c

@@ -90,7 +90,7 @@ static void buf_daemon __P((void));
  * but the code is intricate enough already.
  */
 vm_page_t bogus_page;
-int vmiodirenable = FALSE;
+int vmiodirenable = TRUE;
 int runningbufspace;
 static vm_offset_t bogus_offset;