The omit-needless-words script has grown into a more general "API
dumping" script. Make it a bit more useful by installing it alongside
swift-ide-test, symlinking it in the build directory next to
swift-ide-test (for Swift developers), and defaulting to using the
swift-ide-test in the same directory as the script. Now it's fairly
easy to dump the API for a given SDK with, e.g.,
swift-api-dump.py -s iphoneos