Base tests for 11243: test parsing for md, ei, and ri.

We didn't really have test coverage for these parsing functions, so
I went and made some.  These tests also verify that the parsing
functions set the list of invalid digests correctly.

src/test/include.am

@@ -76,6 +76,8 @@ src_test_bench_LDADD = src/or/libtor.a src/common/libor.a \
 noinst_HEADERS+= \
 	src/test/test.h \
 	src/test/test_descriptors.inc \
+	src/test/example_extrainfo.inc \
+	src/test/failing_routerdescs.inc \
 	src/test/ed25519_vectors.inc
 
 if CURVE25519_ENABLED