Fix build

SDLMain.* not needed with SDL2.
Link WebP ourselves, rather than having it in SDL2_image.framework.
Dependencies: Update cURL to 7.34.0
Dependencies: Update SDL2 to 2.0.3
Dependencies: Update cURL to 7.36.0
Dependencies: Update Vorbis to 1.3.4
Dependencies: Update WebP to 0.4.0
Dependencies: Add libiconv and libintl

libiconv should be at /usr/lib/ on most systems but could be a wrong version and often gets messed up and libintl is not on a clean install so need to bundle them with VDrift. Haven't been able to build these myself, so they are left as dylibs. Had to change the install names (otool -id etc) to make sure they work on other people's systems, and code sign them (codesign -fs - etc). Tested on 10.7 upwards.
Xcode: add uniforms.h to project

VDrift/vdrift@38cfecf