Deal with user specified INSTRUMENT_TYPE

We switch on INSTRUMENT_TYPE to set the internall wrapper
handler. We actually only use this in one spot internally
but we were failing to make a buildable wrapper if you
set the type to something not in our list-of-three.
So for now, warn and default out to internal instrument
for the other types (which is probably the right behavior
for aumf, which is what raised this issue in #271)

src/detail/auv2/build-helper/build-helper.cpp

@@ -331,14 +331,21 @@ int main(int argc, char **argv)
         {
           cppf << "AUV2_Type::aumu_musicdevice";
         }
-        if (u.type == "aumi")
+        else if (u.type == "aumi")
         {
           cppf << "AUV2_Type::aumi_noteeffect";
         }
-        if (u.type == "aufx")
+        else if (u.type == "aufx")
         {
           cppf << "AUV2_Type::aufx_effect";
         }
+        else
+        {
+          std::cout << "   + WARNING: Unable to determine AUV2_Type for instrument type '" << u.type
+                    << "'" << std::endl;
+          std::cout << "     Defaulting to AUV2_Type::musicdevice" << std::endl;
+          cppf << "AUV2_Type::aumu_musicdevice";
+        }
         cppf << "," << args << ", ci) {}"
              << "};\n"
              << "AUSDK_COMPONENT_ENTRY(ausdk::AUMusicDeviceFactory, " << on << ");\n";