Bug#85736: installation fails when using temporary su

[Lee Maguire <lee-debian@hexkey.co.uk>]

Package: libsigc++0
Version: 1.0.2-2
Severity: normal

I use sudo when using apt-get rather than logging in as root.  There are
normally no issues with this, but a recent upgrade of libsigc++0 failed.
This may be die to another package (ldconfig?), but the libsigc++0 is
the first time I've seen any symptoms:

$ sudo apt-get install libsigc++0
Reading Package Lists... Done
Building Dependency Tree... Done
1 packages upgraded, 0 newly installed, 0 to remove and 4 not upgraded.
Need to get 0B/42.4kB of archives. After unpacking 0B will be used.
dpkg: `ldconfig' not found on PATH.
dpkg: `start-stop-daemon' not found on PATH.
dpkg: `install-info' not found on PATH.
dpkg: `update-rc.d' not found on PATH.
dpkg: 4 expected program(s) not found on PATH.
NB: root's PATH should usually contain /usr/local/sbin, /usr/sbin and /sbin.
E: Sub-process /usr/bin/dpkg returned an error code (2)

$ su
Password:
# apt-get install libsigc++0
Reading Package Lists... Done
Building Dependency Tree... Done
1 packages upgraded, 0 newly installed, 0 to remove and 4 not upgraded.
Need to get 0B/42.4kB of archives. After unpacking 0B will be used.
(Reading database ... 61483 files and directories currently installed.)
Preparing to replace libsigc++0 1.0.2-1 (using .../libsigc++0_1.0.2-2_i386.deb) ...
Unpacking replacement libsigc++0 ...
Setting up libsigc++0 (1.0.2-2) ...