progress: enable xmldsig and do other cleanups

error_thunk.go

@@ -1,5 +1,10 @@
 package xmlsec
 
+// onError_cgo is a C function that can be passed to xmlSecErrorsSetCallback which
+// in turn invokes the go function onError which captures the error.
+// For reasons I do not completely understand, it must be defined in a different
+// file from onError
+
 // void onError_cgo(char *file, int line, char *funcName, char *errorObject, char *errorSubject, int reason, char *msg) {
 //   onError(file, line, funcName, errorObject, errorSubject, reason, msg);
 // }