Ship all files needed to build Tor with rust

Fixes bug 25732; bugfix on 0.3.3.2-alpha when strings.rs was
introduced.

changes/bug25732

+  o Minor bugfixes (distribution, compilation):
+    - Actually include all of our Rust source in our source
+      distributions. (Previously, a few of the files were accidentally
+      omitted.) Fixes bug 25732; bugfix on 0.3.3.2-alpha.

src/rust/include.am

@@ -8,6 +8,8 @@ EXTRA_DIST +=\
 	src/rust/external/external.rs \
 	src/rust/external/lib.rs \
 	src/rust/protover/Cargo.toml \
+	src/rust/protover/errors.rs \
+	src/rust/protover/protoset.rs \
 	src/rust/protover/ffi.rs \
 	src/rust/protover/lib.rs \
 	src/rust/protover/protover.rs \
@@ -23,4 +25,5 @@ EXTRA_DIST +=\
 	src/rust/tor_rust/lib.rs \
 	src/rust/tor_util/Cargo.toml \
 	src/rust/tor_util/ffi.rs \
-	src/rust/tor_util/lib.rs
+	src/rust/tor_util/lib.rs \
+	src/rust/tor_util/strings.rs