Ensure embedded profile, if any, is always used

Perform sRGB conversion at end of pipe only

withMetadata exports profile, should not convert

Convert one fixture to sRGB to help test

Discovered while investigating #125

src/metadata.cc

@@ -74,7 +74,7 @@ class MetadataWorker : public NanAsyncWorker {
       baton->height = image->Ysize;
       baton->space = vips_enum_nick(VIPS_TYPE_INTERPRETATION, image->Type);
       baton->channels = image->Bands;
-      baton->hasProfile = (vips_image_get_typeof(image, VIPS_META_ICC_NAME) > 0) ? TRUE : FALSE;
+      baton->hasProfile = HasProfile(image);
       // Derived attributes
       baton->hasAlpha = HasAlpha(image);
       baton->orientation = ExifOrientation(image);