Merge changes from the witness.

src/nvtt/CompressorDXT.h

@@ -26,7 +26,7 @@
 
 #include "Compressor.h"
 
-struct Tile;
+class Tile;
 
 namespace nv
 {

src/nvtt/tests/imperativeapi.cpp

@@ -69,7 +69,7 @@ int main(int argc, char *argv[])
     float gamma = 2.2f;
     image.toLinear(gamma);
 
-    float alphaRef = 0.95;
+    float alphaRef = 0.95f;
     float coverage = image.alphaTestCoverage(alphaRef);
 
     // Build mimaps.