initial ISO9660 metadata support

As was noted by Alexey Shabalin in libosinfo context,
current ALT Linux images tend to lack ISO9660 metadata
-- which they did have back in the day of Master 2.4.

Please note that the data collection occurs this way
due to mkimage's config.mk resetting the values to be
empty; this was worked around by using another config
file, $(BUILDDIR)lib/iso.mk, and including it later
but that would require a separate target with per-target
CONFIG variable which isn't elegant at all given the need
to actually build up the metadata set.

So the variables were changed (to be more readable anyways)
and then proxied back to BOOT_*.  This might be cleaned up
some day after the inclusion order is tweaked or mkimage
defaults get set-if-unset-yet (?=).

features.in/build-distro/README

@@ -1,4 +1,5 @@
 Эта фича конфигурирует создание образа дистрибутива, включая работу
 с субпрофилями -- которая сейчас нужна только дистрибутивным целям.
 
-Дополняет финальную стадию сборки (lib/, scripts.d/).
+Дополняет финальную стадию сборки (lib/, scripts.d/)
+и тесно с ней связана.

features.in/build-distro/lib/build-distro.mk

@@ -4,7 +4,17 @@
 # take the latter part
 SUBDIRS = $(notdir $(SUBPROFILES))
 
-BOOT_TYPE = isolinux
+# proxy over the ISO metadata collected; see also genisoimagerc(5)
+BOOT_SYSI := $(META_SYSTEM_ID)
+BOOT_PUBL := $(META_PUBLISHER)
+BOOT_PREP := $(META_PREPARER)
+BOOT_APPI := $(META_APP_ID)
+BOOT_VOLI := $(META_VOL_ID)
+BOOT_VOLS := $(META_VOL_SET)
+BOOT_BIBL := $(META_BIBLIO)
+BOOT_ABST := $(META_ABSTRACT)
+
+BOOT_TYPE := isolinux
 
 # Metadata/ needed only for installers (and not for e.g. syslinux.iso)
 # FIXME: installable live needs it too, don't move to install2 feature

features.in/build-ve/README

@@ -1,3 +1,4 @@
 Эта фича конфигурирует создание образа виртуального окружения (VE).
 
-Дополняет финальную стадию сборки (lib/, image-scripts.d/).
+Дополняет финальную стадию сборки (lib/, image-scripts.d/)
+и тесно с ней связана.

features.in/dos/config.mk

@@ -1,5 +1,9 @@
+# tries to fill in ISO metadata in case it's the only inhabitant
 use/dos: use/syslinux
 	@$(call add_feature)
 	@$(call add,SYSLINUX_CFG,dos)
 	@$(call add,SYSLINUX_FILES,/usr/lib/syslinux/memdisk)
 	@$(call add,STAGE1_PACKAGES,make-freedos-floppy glibc-gconv-modules)
+	@$(call try,META_SYSTEM_ID,DOS)
+	@$(call try,META_VOL_ID,FreeDOS 2.88M)
+	@$(call try,META_VOL_SET,FreeDOS)

features.in/syslinux/config.mk

@@ -2,6 +2,7 @@
 use/syslinux: sub/stage1
 	@$(call add_feature)
 	@$(call add,STAGE1_PACKAGES,syslinux)
+	@$(call try,META_SYSTEM_ID,SYSLINUX)
 
 # UI is overwritten
 use/syslinux/ui-%: use/syslinux

lib/distro.mk

@@ -16,12 +16,18 @@ boot/%:
 
 # fundamental targets
 
-distro/.init: profile/bare; @:
+distro/.init: profile/bare
+	@$(call try,META_PREPARER,mkimage-profiles)
+	@$(call try,META_APP_ID,$(IMAGE_NAME))
+	@$(call set,META_PUBLISHER,ALT Linux Team)
 
 # NB: the last flavour in KFLAVOURS gets to be the default one;
 # the kernel packages regexp evaluation has to take place at build stage
 distro/.base: distro/.init
 	@$(call set,KFLAVOURS,std-def)
+	@$(call set,META_SYSTEM_ID,LINUX)
+	@$(call set,META_VOL_ID,ALT Linux $(ARCH))
+	@$(call set,META_VOL_SET,ALT Linux)
 
 # something marginally useful (as a network-only installer)
 # NB: doesn't carry stage3 thus cannot use/bootloader