Fix Bullet's btVector3.cpp compile error on 64-bit iOS platform.
See https://code.google.com/p/bullet/source/detail?r=2716
For Travis CI - more tweaks on the packaging setup. [ci package]

- Prevent packaging from being accidentally invoked by a pull request or a commit on non-master branch.
- Generate documentation before packaging if it is not yet generated in previous step.
- When packaging for iOS platform, rebuild Urho3D library as Mach-O universal binary.
- When packaging for Linux platform, also invokes RPM and Debian CPack generators.
For Travis CI - switch CI build to use OS X build environment.