If you're exporting your Android application with the Android plugin, the plugin already specifies a standard configuration for you. This configuration includes the basic -keep options and all the necessary -injars and -outjars options (hence the note about duplicate class definitions). This means that your proguard-project.txt file can be empty to begin with; it should only contain any project-specific configuration.
The warnings explain that the Foursquare library refers to the AppEngine library and even to the servlet library, but these latter libraries are missing from your project. That's not a problem, since your app presumably works fine in debug mode, without these libraries, so you can tell ProGuard to ignore these issues:
-dontwarn fi.foyt.foursquare.**
See the ProGuard manual > Troubleshooting > Warning: can't find referenced class