Update to support rust-protobuf v1.6.0

* Updated `proto/proof.rs` using the latest stable protoc (3.5.1) and protoc-gen-rust
  plugin (1.6.0).
  * I had to make a tiny manual modification to `proto/proof.rs`. On line 298 I
    added derivation of `Debug` in order to satisfy the lint directive in
    `lib.rs`.
* `bytes` protobuf fields are empty if the message doesn't contain the
  corresponding element, so since methods are no longer provided to directly
  check, we use `is_empty()` on the corresponding struct fields.

Author: psivesely

Cargo.toml

@@ -19,7 +19,7 @@ categories    = ["data-structures", "cryptography"]
 
 [dependencies]
 ring = "^0.12.0"
-protobuf = { version = "^1.4.0", optional = true }
+protobuf = { version = "^1.6.0", optional = true }
 
 [features]
 serialization-protobuf = [ "protobuf" ]

src/proto/mod.rs

@@ -8,7 +8,7 @@ pub use self::proof::{ProofProto, LemmaProto};
 
 use protobuf::Message;
 use protobuf::error::ProtobufResult;
-use protobuf::core::parse_from_bytes;
+use protobuf::parse_from_bytes;
 
 impl<T> Proof<T> {
     /// Constructs a `Proof` struct from its Protobuf representation.
@@ -80,7 +80,7 @@ impl ProofProto {
         T: From<Vec<u8>>,
     {
 
-        if !self.has_root_hash() || !self.has_lemma() {
+        if self.root_hash.is_empty() || !self.has_lemma() {
             return None;
         }
 
@@ -125,7 +125,7 @@ impl LemmaProto {
     }
 
     pub fn into_lemma(mut self) -> Option<Lemma> {
-        if !self.has_node_hash() {
+        if self.node_hash.is_empty() {
             return None;
         }