Front-end: Add a function selector under implicit type conversion.

Use the new function selector for #version 400 and above,
parameterized for the GLSL #version 400 selection rules.

This can be used for both GLSL and HLSL, and other languages
as well.

Test/400.vert

@@ -4,6 +4,103 @@ in double d;   // ERROR, no doubles
 in dvec3 d3;   // ERROR, no doubles
 in dmat4 dm4;  // ERROR, no doubles
 
-void main()
-{
+// function selection under type conversion
+void foo1(double a, uint b)  {}
+void foo1(double a, int b)   {}
+void foo1(double a, float b) {}
+void foo1(double a, double b){}
+
+void foo2(double a, float b) {}
+void foo2(double a, double b){}
+
+void foo3(double a, float b) {}
+void foo3(float a, double b) {}
+
+void ftd(  int,  float, double) {}
+void ftd( uint,  float, double) {}
+void ftd(float, double, double) {}
+
+void main()
+{
+    double d;
+	uint u;
+	int i;
+	float f;
+
+	foo1(d, d);
+	foo1(d, u);
+	foo1(d, i);
+	foo1(d, f);
+
+	foo1(f, d);
+	foo1(f, u);
+	foo1(f, i);
+	foo1(f, f);
+
+	foo1(u, d);
+	foo1(u, u);
+	foo1(u, i);
+	foo1(u, f);
+
+	foo1(i, d);
+	foo1(i, u);
+	foo1(i, i);
+	foo1(i, f);
+
+	foo2(d, d);
+	foo2(d, u);
+	foo2(d, i);
+	foo2(d, f);
+
+	foo2(f, d);
+	foo2(f, u);
+	foo2(f, i);
+	foo2(f, f);
+
+	foo2(u, d);
+	foo2(u, u);
+	foo2(u, i);
+	foo2(u, f);
+
+	foo2(i, d);
+	foo2(i, u);
+	foo2(i, i);
+	foo2(i, f);
+
+	foo3(d, d);  // ERROR, no match
+	foo3(d, u);
+	foo3(d, i);
+	foo3(d, f);
+
+	foo3(f, d);
+	foo3(f, u); // ERROR, ambiguous
+	foo3(f, i); // ERROR, ambiguous
+	foo3(f, f); // ERROR, ambiguous
+
+	foo3(u, d);
+	foo3(u, u); // ERROR, ambiguous
+	foo3(u, i); // ERROR, ambiguous
+	foo3(u, f); // ERROR, ambiguous
+
+	foo3(i, d);
+	foo3(i, u); // ERROR, ambiguous
+	foo3(i, i); // ERROR, ambiguous
+	foo3(i, f); // ERROR, ambiguous
+
+	ftd(i, f, f);
+	ftd(u, f, f);
+}
+
+void itf(int, float, int);
+void itf(int, double, int);
+
+void tf()
+{
+    double d;
+	uint u;
+	int i;
+	float f;
+	
+	itf(i, i, i);
+	itf(i, u, i);
 }