We already link SDL2_test by default now.
Added some extra protection to notify the developer if they haven't initialized the application properly.

This will help reduce issues like that reported in bug 1819:

Wouter van Oortmerssen 2013-04-23 20:12:07 EDT
#0  0x01d1e881 in __HALT ()
#1  0x01c58971 in _CFRuntimeCreateInstance ()
#2  0x02e4acc1 in GSFontCreateWithName ()
#3  0x00adc0e1 in UINewFont ()
#4  0x00adc24c in +[UIFont systemFontOfSize:traits:] ()
#5  0x00adc298 in +[UIFont systemFontOfSize:] ()
#6  0x009fb5d9 in +[UITextFieldLabel defaultFont] ()
#7  0x00a8ccd5 in -[UILabel _commonInit] ()
#8  0x00a8ce14 in -[UILabel initWithFrame:] ()
#9  0x00a052eb in -[UITextField createTextLabelWithTextColor:] ()
#10 0x009fbede in -[UITextField initWithFrame:] ()
#11 0x00152ead in -[SDL_uikitview initializeKeyboard] at /Users/aardappel/lobster/external/SDL-2.0.0-7046/Xcode-iOS/SDL/../../src/video/uikit/SDL_uikitview.m:208
#12 0x0015290c in -[SDL_uikitview initWithFrame:] at /Users/aardappel/lobster/external/SDL-2.0.0-7046/Xcode-iOS/SDL/../../src/video/uikit/SDL_uikitview.m:50
#13 0x00153b5b in -[SDL_uikitopenglview initWithFrame:scale:retainBacking:rBits:gBits:bBits:aBits:depthBits:stencilBits:majorVersion:] at /Users/aardappel/lobster/external/SDL-2.0.0-7046/Xcode-iOS/SDL/../../src/video/uikit/SDL_uikitopenglview.m:53
#14 0x001524ff in UIKit_GL_CreateContext at /Users/aardappel/lobster/external/SDL-2.0.0-7046/Xcode-iOS/SDL/../../src/video/uikit/SDL_uikitopengles.m:114
#15 0x0015078f in SDL_GL_CreateContext at /Users/aardappel/lobster/external/SDL-2.0.0-7046/Xcode-iOS/SDL/../../src/video/SDL_video.c:2666
#16 0x000d8c5c in SDLInit(char const*, vec<int, 2>&) at /Users/aardappel/lobster/dev/xcode/lobster/../../src/sdlsystem.cpp:193
This patch isn't needed because you have the window and can do [nswindow contentView] yourself.
I'm rolling this back so we minimize the things exposed that we have to keep consistent in the API.
Need to include SDL_main.h when we call SDL_main()
The jump hack is no longer used.

Cheers!
Fixed compile errors on iOS