Add support for including symbolic links in the zip file for the applcia...

...tion (as opposed to including multiple copies of the files that the symbolic links point to).  This can result in a significantly smaller zip file for applications that use frameworks, libraries, or packages that include symbolic links -- in a small PyQt5 application under MacOS X, including symbolic links in the zip file reduced its size from 42 MB down to 30 MB.

Tested under: esky:master, py2app 0.8.1, PyQt 5.3, Qt 5.3.0 open source, Python 2.7.6 (local build), XCode 5.1.1, MacOS X 10.9.3.