Don't clobber refcounting in SDL_Init.

- Fixes bug 1712 by not overwriting SDL_SubsystemRefCount in SDL_Init.
       - Removes the SDL_initialized variable, and makes SDL_SubsystemRefCount
         the canonical source of truth for whether or not a subsystem has been
         initialized.
       - Refactors SDL_InitSubSystem and SDL_QuitSubSystem to use helper
         functions to manage refcount.
       - Adds automated tests for SDL_Init/Quit*.
       - Adds SDL_bits.h which contains SDL_MostSignificantBitIndex.

VisualC/SDL/SDL_VS2008.vcproj

@@ -375,6 +375,10 @@
 				RelativePath="..\..\include\SDL_audio.h"
 				>
 			</File>
+			<File
+				RelativePath="..\..\include\SDL_bits.h"
+				>
+			</File>
 			<File
 				RelativePath="..\..\include\SDL_blendmode.h"
 				>

VisualC/SDL/SDL_VS2010.vcxproj

@@ -207,6 +207,7 @@
     <ClInclude Include="..\..\include\SDL_assert.h" />
     <ClInclude Include="..\..\include\SDL_atomic.h" />
     <ClInclude Include="..\..\include\SDL_audio.h" />
+    <ClInclude Include="..\..\include\SDL_bits.h" />
     <ClInclude Include="..\..\include\SDL_blendmode.h" />
     <ClInclude Include="..\..\include\SDL_clipboard.h" />
     <ClInclude Include="..\..\include\SDL_config.h" />

VisualC/SDL/SDL_VS2012.vcxproj

@@ -211,6 +211,7 @@
     <ClInclude Include="..\..\include\SDL_assert.h" />
     <ClInclude Include="..\..\include\SDL_atomic.h" />
     <ClInclude Include="..\..\include\SDL_audio.h" />
+    <ClInclude Include="..\..\include\SDL_bits.h" />
     <ClInclude Include="..\..\include\SDL_blendmode.h" />
     <ClInclude Include="..\..\include\SDL_clipboard.h" />
     <ClInclude Include="..\..\include\SDL_config.h" />
@@ -454,4 +455,4 @@
   <Import Project="$(VCTargetsPath)\Microsoft.Cpp.targets" />
   <ImportGroup Label="ExtensionTargets">
   </ImportGroup>
-</Project>
+</Project>