Why can I no longer (un)install packages via apt-get after doing a partial dist-upgrade?

I (stupidly) ran sudo apt-get dist-upgrade, which partially succeeded, but now I get output similar to this every time I try to (un)install a package:

Here, for instance, is the output of sudo apt-get autoremove --purge postgres*:

Removing linux-image-extra-3.13.0-43-generic (3.13.0-43.72) ...
run-parts: executing /etc/kernel/postinst.d/apt-auto-removal 3.13.0-43-generic /boot/vmlinuz-3.13.0-43-generic
run-parts: executing /etc/kernel/postinst.d/dkms 3.13.0-43-generic /boot/vmlinuz-3.13.0-43-generic
run-parts: executing /etc/kernel/postinst.d/initramfs-tools 3.13.0-43-generic /boot/vmlinuz-3.13.0-43-generic
update-initramfs: Generating /boot/initrd.img-3.13.0-43-generic
W: mdadm: the array /dev/md/monolith:0 with UUID 826ef9b8:1c282186:82586683:e0b960b3
W: mdadm: is currently active, but it is not listed in mdadm.conf. if
W: mdadm: it is needed for boot, then YOUR SYSTEM IS NOW UNBOOTABLE!
W: mdadm: please inspect the output of /usr/share/mdadm/mkconf, compare
W: mdadm: it to /etc/mdadm/mdadm.conf, and make the necessary changes.
run-parts: executing /etc/kernel/postinst.d/pm-utils 3.13.0-43-generic /boot/vmlinuz-3.13.0-43-generic
run-parts: executing /etc/kernel/postinst.d/update-notifier 3.13.0-43-generic /boot/vmlinuz-3.13.0-43-generic
run-parts: executing /etc/kernel/postinst.d/zz-update-grub 3.13.0-43-generic /boot/vmlinuz-3.13.0-43-generic
/usr/sbin/grub-mkconfig: 38: /etc/default/grub: function: not found
run-parts: /etc/kernel/postinst.d/zz-update-grub exited with return code 127
dpkg: error processing package linux-image-extra-3.13.0-43-generic (--remove):
 subprocess installed post-removal script returned error exit status 1
Errors were encountered while processing:
 linux-image-extra-3.13.0-43-generic
E: Sub-process /usr/bin/dpkg returned an error code (1)

Here's the output of /usr/share/mdadm/mkconf:

# mdadm.conf
#
# Please refer to mdadm.conf(5) for information about this file.
#

# by default (built-in), scan all partitions (/proc/partitions) and all
# containers for MD superblocks. alternatively, specify devices to scan, using
# wildcards if desired.
#DEVICE partitions containers

# auto-create devices with Debian standard permissions
CREATE owner=root group=disk mode=0660 auto=yes

# automatically tag new arrays as belonging to the local system
HOMEHOST <system>

# instruct the monitoring daemon where to send mail alerts
MAILADDR root

# definitions of existing MD arrays

And here's the output of /etc/mdadm/mdadm.conf:

# mdadm.conf
#
# Please refer to mdadm.conf(5) for information about this file.
#

# by default (built-in), scan all partitions (/proc/partitions) and all
# containers for MD superblocks. alternatively, specify devices to scan, using
# wildcards if desired.
#DEVICE partitions containers

# auto-create devices with Debian standard permissions
CREATE owner=root group=disk mode=0660 auto=yes

# automatically tag new arrays as belonging to the local system
HOMEHOST <system>

# instruct the monitoring daemon where to send mail alerts
MAILADDR root

# definitions of existing MD arrays
ARRAY /dev/md/0 metadata=1.2 UUID=c13ebb40:55db4a69:108822c5:5ee02f0b name=htpc:0

# This file was auto-generated on Thu, 11 Jun 2015 00:15:47 +0200
# by mkconf $Id$

What's my next move?

Edit: It should be noted that I have no problem rebooting, as I'm not booting to RAID.

Solution 1:

Running

cp /usr/share/grub/default/grub /etc/default/grub
update-grub
sudo apt-get -f install

seems to have fixed the issue. I'm still not exactly sure why things got screwy in the first place, but hopefully this might save someone else's butt...