Make looking for "deps" optional and per-platform. If you are building for several platforms in one allegro repo the deps get mixed up, i.e. OSX will pick up iOS libraries. Added AL_DEPS, which can be set in the iPhone toolchain for iPhone dependencies.

Fixes to apple_build.sh:
* Static library flag was set incorrectly so broken on OSX.
* Renamed the "install" section "universal" as we are creating universal binaries. Probably need to add an install section at some point.