syslinux: update rw to use cdrom method, not disk

The former approach to handling "LiveCD with sessions"
has been to mangle "automatic=method:cdrom" into
"automatic=method:disk,label:ALT*" within gfxboot
so that propagator and make-initrd-propagator would
try and discover/create a filesystem labelled
"alt-live-storage" on a LiveFlash's free space.

Then "live_rw" handling has been unified in
make-initrd-propagator (as of 0.18-alt1) to accept
any of "label" subparameter or "live_rw" argument
to go and create_disk_slice().

Then propagator's cdrom.c has been fixed to actually
try sdX1 before sdX (as of 20150306-alt1).

And now it's all been tested to verify that:
- flash "ro" and "rw" boot is OK
- CD-ROM "ro" boot is OK
- CD-ROM "rw" boot is fine given that there's
  a partition labeled "alt-live-storage" elsewhere

This is a can of worms indeed :-/

References
~~~~~~~~~~
* http://altlinux.org/initrd-propagator
* http://altlinux.org/make-initrd-propagator
* http://bugzilla.altlinux.org/28289

features.in/syslinux/cfg.in/32live_rw.cfg

@@ -1,5 +1,5 @@
 label session
   menu label LiveCD with ^sessions support
   kernel alt0/vmlinuz
-  append initrd=alt0/full.cz fastboot live showopts automatic=method:disk,label:ALT* ramdisk_size=@live_size@ stagename=live live_rw vga=0x314 @bootargs@
+  append initrd=alt0/full.cz fastboot live showopts automatic=method:cdrom ramdisk_size=@live_size@ stagename=live live_rw vga=0x314 @bootargs@
 

features.in/syslinux/cfg.in/82rescue_rw.cfg

@@ -1,6 +1,5 @@
 label rescue_session
   menu label Rescue with sess^ions support
   kernel alt0/vmlinuz
-  append initrd=alt0/full.cz fastboot live showopts automatic=method:disk,label:ALT* ramdisk_size=@rescue_size@ stagename=rescue live_rw
-
+  append initrd=alt0/full.cz fastboot live showopts automatic=method:cdrom ramdisk_size=@rescue_size@ stagename=rescue live_rw