We now generate info.plist during the build. There are multiple ways
to do this, but I settled on invoking sed from a Makefile. The problems
with other possible ways were:

- Although we could have used simple substitution from configure, this
  would not include the last modification year. This could have been added
  to configure, but we probably also want this to update within a make
  clean - make cycle without re-running configure. For git-version.h
  this is also done from a Makefile and not configure.
- Using the C preprocessor (that XCode apparently does) to generate
  info.plist did not work properly.
- Using PListBuddy would reorder the entire info.plist file, making it
  hard to inspect the changes made as a human.