Mid-rule actions are simply... ignored!

* src/reader.c (readgram): Be sure to attach mid-rule actions to
the empty-rule associated to the dummy symbol, not to the host
rule.
* tests/actions.at (Mid-rule actions): New.

tests/testsuite.at

@@ -28,6 +28,7 @@ AT_TESTED([bison])
 m4_include([output.at])
 m4_include([sets.at])
 m4_include([reduce.at])
+m4_include([actions.at])
 m4_include([calc.at])
 m4_include([torture.at])
 m4_include([regression.at])