Write JPEG image with correct orientation.

src/partiviewc.cc

@@ -650,7 +650,7 @@ static int snapjpeg( char *outfname, int xsize, int ysize, char *rgbbuf )
 
     while(cinfo.next_scanline < cinfo.image_height) {
 	JSAMPROW rowptr[1];
-	rowptr[0] = reinterpret_cast<JSAMPROW>(&rgbbuf[cinfo.next_scanline * xsize*3]);
+	rowptr[0] = reinterpret_cast<JSAMPROW>(&rgbbuf[(cinfo.image_height - 1 - cinfo.next_scanline) * xsize*3]);
 	jpeg_write_scanlines(&cinfo, rowptr, 1);
     }
     jpeg_finish_compress(&cinfo);