Requery the parse table when breaking down the parse stack on invalid lookahead (#636)

* Requery parse table after breaking down parse stack due to invalid lookahead

* Include Ruby parser in randomized test suite

Ruby and PHP are our only two languages that use non-terminal extras.
Adding Ruby uncovered some bugs.

* Print edited source code when running parse --edit w/ debug flag

* Recompute lookahead when breaking down stack on invalid lookahead

* Fix stack summary leak when there are two discontinuities on a stack version

cli/src/tests/corpus_test.rs

@@ -24,6 +24,7 @@ const LANGUAGES: &'static [&'static str] = &[
     "json",
     "php",
     "python",
+    "ruby",
     "rust",
 ];