SUGGESTED FIX

1. downloaded and installed xcode to 4.3.3 on build machines
   -- at the end of installation, removed the old 4.2 installation
2. downloaded and installed command line tool
3, downloaded and installed auxiliary tool (to get PackageMaker)
   -- PackageMaker is a separate installation. Get it from:
http://adcdownload.apple.com/Developer_Tools/auxiliary_tools_for_xcode__february_2012/auxiliary_tools_for_xcode.dmg

Double-click on the disk image.

-- From a terminal window, open up the Applications folder inside Xcode so it shows up in the Finder. 

% open /Applications/Xcode.app/Contents/Applications/

Copy PackageMaker.app from the disk image to here.

-- Create symlinks so the install part of the build will work.

% cd /Applications/Xcode.app/Contents/Developer/usr/bin
% ln -s /Applications/Xcode.app/Contents/Applications/PackageMaker.app/Contents/MacOS/PackageMaker
% ln -s /usr/libexec/PlistBuddy

-- For the signing part of the build, use 

% productsign --sign "Developer ID Installer" --keychain InstallerSigning.keychain /path/to/.pkg /path/to/output_file
                                     

EVALUATION

According to Scott, we'll need to sign the .pkg with apple's certificate and
before it's bundled into the .dmg.