dpkg --set-selections failing silently

[Nick Cabatoff <ncc@cs.mcgill.ca>]

This is with slink's dpkg.  For reasons I don't understand, some
packages don't get set by --set-selections and no explanation is
given.  Currently I've only noticed this with libpng2-dev, librx1g-dev
and zlib1g-dev.  Example:

flanders:/usr/local# dpkg --get-selections |grep png
libpng0g                                        install
libpng2                                         install
pnmtopng                                        install
flanders:/usr/local# echo libpng2-dev install |dpkg --set-selections
flanders:/usr/local# dpkg --get-selections |grep png
libpng0g                                        install
libpng2                                         install
pnmtopng                                        install

I've had similar problems when missing dependancies were at issue, but
that doesn't seem to be the case here:

flanders:/usr/local# apt-get install -d libpng2-dev 
Reading Package Lists... Done
Building Dependency Tree... Done
The following extra packages will be installed:
  zlib1g-dev 
The following NEW packages will be installed:
  libpng2-dev zlib1g-dev 
0 packages upgraded, 2 newly installed, 0 to remove and 21 not
upgraded.
2 packages not fully installed or removed.
Need to get 0B/264kB of archives. After unpacking 829kB will be used.
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