Change how getReferenceCommit() retrieves commits

If a tag is annotated, its target() will return a tag object instead
of the tag's underlying commit. This causes Repository's
getReferenceCommit() to not work as it will try to find a commit
based on the tag's oid. By replacing target() with peel(), the code
can now find the actual underlying commit regardless of whether a tag
is annotated or not.

Signed-off-by: Remy Suen <remy.suen@gmail.com>

lib/repository.js

@@ -1055,10 +1055,8 @@ Repository.prototype.getReference = function(name, callback) {
  * @return {Commit}
  */
 Repository.prototype.getReferenceCommit = function(name, callback) {
-  var repository = this;
-
   return this.getReference(name).then(function(reference) {
-    return repository.getCommit(reference.target()).then(function(commit) {
+    return reference.peel(NodeGit.Object.TYPE.COMMIT).then(function(commit) {
       if (typeof callback === "function") {
         callback(null, commit);
       }

test/tests/repository.js

@@ -327,4 +327,40 @@ describe("Repository", function() {
         assert.equal(numMergeHeads, 1);
       });
   });
+
+  it("can get reference commit that points at lightweight tag", function() {
+    var repository = this.repository;
+    var oid = null;
+    return repository.getHeadCommit()
+      .then(function(commit) {
+        oid = commit.id().toString();
+        return repository.createLightweightTag(
+          oid, "getReferenceCommitLightweight");
+      })
+      .then(function() {
+        return repository.getReferenceCommit(
+          "refs/tags/getReferenceCommitLightweight");
+      })
+      .then(function(commit) {
+        assert.equal(commit.id().toString(), oid);
+      });
+  });
+
+  it("can get reference commit that points at annotated tag", function() {
+    var repository = this.repository;
+    var oid = null;
+    return repository.getHeadCommit()
+      .then(function(commit) {
+        oid = commit.id().toString();
+        return repository.createTag(
+          oid, "getReferenceCommitAnnotated", "");
+      })
+      .then(function() {
+        return repository.getReferenceCommit(
+          "refs/tags/getReferenceCommitAnnotated");
+      })
+      .then(function(commit) {
+        assert.equal(commit.id().toString(), oid);
+      });
+  });
 });