Added the ability to set SDL hints from AndroidManifest.xml (thanks Rachel!)

This is especially useful for things like the accelerometer hint which could be needed before application main().

src/core/android/SDL_android.h

@@ -59,6 +59,9 @@ size_t Android_JNI_FileRead(SDL_RWops* ctx, void* buffer, size_t size, size_t ma
 size_t Android_JNI_FileWrite(SDL_RWops* ctx, const void* buffer, size_t size, size_t num);
 int Android_JNI_FileClose(SDL_RWops* ctx);
 
+/* Environment support */
+char *SDL_AndroidGetManifestEnvironmentVariable(const char *variableName);
+
 /* Clipboard support */
 int Android_JNI_SetClipboardText(const char* text);
 char* Android_JNI_GetClipboardText(void);