Removed alloca calls from sound reader classes because putting it inside a loop tends to cause a stack overflow.

Removed alloca call from png loading because it does not work with setjmp and longjmp.  png loading now uses exceptions instead when an error occurs.

src/RageSoundReader_Resample_Good.cpp

@@ -667,8 +667,7 @@ int RageSoundReader_Resample_Good::Read( float *pBuf, int iFrames )
 
 	{
 		int iFramesNeeded = m_apResamplers[0]->NumInputsForOutputSamples(iFrames);
-		float *pTmpBuf = (float *) alloca( iFramesNeeded * sizeof(float) * iChannels );
-		ASSERT( pTmpBuf != NULL );
+		float pTmpBuf[iFramesNeeded * iChannels];
 		int iFramesIn = m_pSource->Read( pTmpBuf, iFramesNeeded );
 		if( iFramesIn < 0 )
 			return iFramesIn;