grub2|loopback: fix theme issues for submenus

also enables greater flexibility for users to override more aspects of
theme separate from menu entries, and similarly the initial config details
separate from the menu entries. (with the recent change to merge user files
with the defaults rather than replace them, users can pick which of these
individual components they wish to customise.

identical to change as sent in to Kali and accepted by Raphaël.

Gbp-Dch: Short

share/bootloaders/grub-pc/config.cfg

@@ -0,0 +1,16 @@
+set default=0
+
+loadfont $prefix/dejavu-bold-16.pf2
+loadfont $prefix/dejavu-bold-14.pf2
+loadfont $prefix/unicode.pf2
+set gfxmode=auto
+insmod all_video
+insmod gfxterm
+insmod png
+
+source /boot/grub/theme.cfg
+
+terminal_output gfxterm
+
+insmod play
+play 960 440 1 0 4 440 1

share/bootloaders/grub-pc/grub.cfg

@@ -1,31 +1,4 @@
-set default=0
-
-loadfont $prefix/dejavu-bold-16.pf2
-loadfont $prefix/dejavu-bold-14.pf2
-loadfont $prefix/unicode.pf2
-set gfxmode=auto
-insmod all_video
-insmod gfxterm
-insmod png
-
-set color_normal=light-gray/black
-set color_highlight=white/dark-gray
-
-if [ -e /isolinux/splash.png ]; then
-    # binary_syslinux modifies the theme file to point to the correct
-    # background picture
-    set theme=/boot/grub/live-theme/theme.txt
-elif [ -e /boot/grub/splash.png ]; then
-    set theme=/boot/grub/live-theme/theme.txt
-else
-    set menu_color_normal=cyan/blue
-    set menu_color_highlight=white/blue
-fi
-
-terminal_output gfxterm
-
-insmod play
-play 960 440 1 0 4 440 1
+source /boot/grub/config.cfg
 
 # Live boot
 @LINUX_LIVE@
@@ -51,6 +24,8 @@ source	/boot/grub/install_start.cfg
 
 submenu 'Advanced install options...' --hotkey=a {
 
+	source /boot/grub/theme.cfg
+
 	source	/boot/grub/install.cfg
 
 }
@@ -59,6 +34,8 @@ fi
 if @ENABLE_MEMTEST@; then
 submenu 'Advanced options...' {
 
+	source /boot/grub/theme.cfg
+
 	# Memtest (if any)
 	source	/boot/grub/memtest.cfg
 

share/bootloaders/grub-pc/theme.cfg

@@ -0,0 +1,13 @@
+set color_normal=light-gray/black
+set color_highlight=white/dark-gray
+
+if [ -e /isolinux/splash.png ]; then
+    # binary_syslinux modifies the theme file to point to the correct
+    # background picture
+    set theme=/boot/grub/live-theme/theme.txt
+elif [ -e /boot/grub/splash.png ]; then
+    set theme=/boot/grub/live-theme/theme.txt
+else
+    set menu_color_normal=cyan/blue
+    set menu_color_highlight=white/blue
+fi