I'm not sure if it is acceptable for rubygems to skip loaded features.

+VALUE
+rb_f_loaded_feature(VALUE obj, VALUE fname)
+{
+  return rb_provided(RSTRING_PTR(rb_str_encode_ospath(fname))) ? Qtrue : Qfalse;
+}

Why is this function global?
And the argument of RSTRING_PTR should not have side effects.