HLSL: matrix swizzle (_12, _m23) syntax, partial semantics.

This partially addressess issue #670, for when the matrix swizzle
degenerates to a component or column: m[c], m[c][r] (where HLSL
swaps rows and columns for user's view).

An error message is given for the arbitrary cases not covered.

These cases will work for arbitrary use of l-values.

Future work will handle more arbitrary swizzles, which might
not work as arbitrary l-values.

Test/hlsl.matrixSwizzle.vert

@@ -0,0 +1,10 @@
+void ShaderFunction(float inf) : COLOR0
+{
+    float3x4 m;
+
+    m._34  = 1.0; // AST should have a normal component select
+    m._m23 = 2.0; // same code
+
+    m._11_12_13_14 = float4(3.0);      // AST should have normal column selection (first row)
+    m._m10_m11_m12_m13 = float4(3.0);  // AST should have normal column selection (second row)
+}