osx makefile: fix typo, point CFBundleExecutable at the actual exe, and update the display names to reflect just the app name and not its path in the build tree.

With this patch, apps can be run successfully via double click in the Finder (or with `open mydemo.app`), whereas previously it was required to invoke the internal exe directly via command line or other.
Merge pull request #2641 from liamstask/osx-makefile-fix

osx makefile: fix typo, point CFBundleExecutable at the actual exe, and ...