Add BC7 support. It's incredibly slow - ~60 seconds to compress a 512x512 image, on a Core i7 - but it works.

- Added AVPCL compressor to projects and got it building with VC9 and VC10.
- Removed unused command line interface & file read/write code from AVPCL.
- Convert AVPCL to use NV vector math lib, asserts, etc.
- Convert AVPCL to use double instead of float.
- Added 4x4 symmetric eigensolver, for AVPCL; it's based on the existing 3x3 one, but I had to rewrite the Householder reduction stage.  As with ZOH, using the eigensolver (instead of SVD) gives a ~25% speedup without significantly affecting RMSE.
- Encapsulate ZOH and AVPCL stuff into their own namespaces to keep everything separate.
- Added some missing vector operators to the nvmath lib.

src/nvtt/Context.cpp

@@ -775,8 +775,7 @@ CompressorInterface * Compressor::Private::chooseCpuCompressor(const Compression
     }
     else if (compressionOptions.format == Format_BC7)
     {
-		// !!!UNDONE
-        //return new CompressorBC7;
+        return new CompressorBC7;
     }
 
     return NULL;