Port macdeployqtplus to OSX 10.8

Use 'osascript' to run AppleScript, instead of using (broken-in-10.8)
python appscript package.

And added support for code-signing the .app bundle, to make OSX's
GateKeeper happy.
Code-signing certificates (no private keys) from Apple and Comodo
Merge pull request #2179 from gavinandresen/osx_codesign

Update mac packaging tool to create code-signed .app packages