Added test case for GitHub ldc-developers/ldc#497.

Author: dnadlinger

compilable/ldc_github_497.d

@@ -0,0 +1,13 @@
+import std.algorithm : all, canFind;
+
+struct Foo {
+    float a, b, c;
+
+    auto opDispatch(string swiz)() if (swiz.all!(x => "abc".canFind(x))) {
+        return mixin("Foo(" ~ swiz[0] ~ "," ~ swiz[1] ~ "," ~ swiz[2] ~ ")");
+    }
+}
+
+auto f(Foo f) {
+    return f.cab;
+}