Debian: Satisfy GRUB dependencies from stable

jwittlincohen said:
 The Howto instructs users to install grub-pc from Testing, but the
 command used also installs all of its dependencies from Testing, even
 though they can be satisfied from Stable. One of the consequences of
 this is that a version of libfuse2 is installed which is incompatible
 with Gnome and even the more limited Gnome-Core. I'm sure there are
 other package management issues but this is the only one I ran into.

Closes #5851

Debian-Jessie-Root-on-ZFS.md

@@ -227,8 +227,11 @@ Choose one of the following options:
 
 4.6a  Install GRUB for legacy (MBR) booting
 
+    # apt install --yes grub-pc
     # apt install --yes -t testing grub-pc
 
+This intentionally installs GRUB twice: once from `stable` and then from `testing`.  This ensures that dependencies are satisfied from `stable`, if possible, which avoids some conflicts with other packages.
+
 4.6b  Install GRUB for UEFI booting
 
     # apt install dosfstools
@@ -238,8 +241,11 @@ Choose one of the following options:
           /dev/disk/by-id/scsi-SATA_disk1-part3) \
           /boot/efi vfat defaults 0 1 >> /etc/fstab
     # mount /boot/efi
+    # apt install --yes grub-efi-amd64
     # apt install --yes -t testing grub-efi-amd64
 
+This intentionally installs GRUB twice: once from `stable` and then from `testing`.  This ensures that dependencies are satisfied from `stable`, if possible, which avoids some conflicts with other packages.
+
 4.7  Set a root password
 
     # passwd