Correct spelling mistakes.

code/renderercommon/tr_image_png.c

@@ -571,7 +571,7 @@ static uint32_t DecompressIDATs(struct BufferedFile *BF, uint8_t **Buffer)
 		{
 			/*
 			 *  Rewind to the start of this adventure
-			 *  and return unsuccessfull
+			 *  and return unsuccessful
 			 */
 
 			BufferedFileRewind(BF, BytesToRewind);
@@ -754,7 +754,7 @@ static uint32_t DecompressIDATs(struct BufferedFile *BF, uint8_t **Buffer)
 	ri.Free(CompressedData);
 
 	/*
-	 *  Check if the last puff() was successfull.
+	 *  Check if the last puff() was successful.
 	 */
 
 	if(!((puffResult == 0) && (puffDestLen > 0)))

code/renderercommon/tr_public.h

@@ -151,7 +151,7 @@ typedef struct {
 	void	(*CM_DrawDebugSurface)( void (*drawPoly)(int color, int numPoints, float *points) );
 
 	// a -1 return means the file does not exist
-	// NULL can be passed for buf to just determine existance
+	// NULL can be passed for buf to just determine existence
 	int		(*FS_FileIsInPAK)( const char *name, int *pCheckSum );
 	long		(*FS_ReadFile)( const char *name, void **buf );
 	void	(*FS_FreeFile)( void *buf );

code/renderercommon/tr_types.h

@@ -173,7 +173,7 @@ typedef enum {
 } glDriverType_t;
 
 typedef enum {
-	GLHW_GENERIC,			// where everthing works the way it should
+	GLHW_GENERIC,			// where everything works the way it should
 	GLHW_3DFX_2D3D,			// Voodoo Banshee or Voodoo3, relevant since if this is
 							// the hardware type then there can NOT exist a secondary
 							// display adapter