Qt5.4.0 Beta: Mac installer is not signed for OS X 10.9.5+

Launching the installer brings up the "unidentified developer" dialog. The workaround is to option-click to get the "Run" override dialog.

OS X 10.9.5 and 10.10 requires version 2 code signatures. See https://developer.apple.com/library/prerelease/mac/technotes/tn2206/_index.html#//apple_ref/doc/uid/DTS40007919-CH1-TNTAG205 .

We probably need to do this:
1) run the code signing tool on a 10.9.5 system
2) fix the app bundle structure (as done by qmake in recent versions of Qt)

Test with "spctl":

spctl -a -t exec -vv qt-enterprise-mac-x64-clang-5.3.2.app
qt-enterprise-mac-x64-clang-5.3.2.app: rejected
source=obsolete resource envelope