Testing of the Mac version of the jpeg-to-pdf app demonstrated that it was now broken, presumably because of some change to OSX since last May. After much pain and suffering involving getting a fresh version of Platypus installed and doing a lot of testing, we have ended up with a new version of the .app file which works. Lessons learned:

• Platypus settings should include bash as the executor, but check those settings manually; when I just accepted the default, the result was an app which tried to execute bash from inside bash (I think).
• Do the build on a Mac (obviously), and make sure the result is committed to svn from a Mac, otherwise stuff gets broken (the .app is actually a folder, and is treated like one by every other OS).
• Add another zipped version to svn just to be safe.
• Use the Cactus DMG distro of ImageMagick rather than trying to install it from Mac Ports or using binaries.