Add Id for PullRequest.cs (#1537)

* add Id for PullRequest.cs

added the Id property for PullRequest model

* use long for pull request id

* update comments for PullRequest.Id and Issue.Id

make it more intuitive... a question, issue.Id and comment.Id are int
type. do we have any concern on it?

* plus the one for pullrequest

forgot to check this change.

* update the integration test for Id Property

long will never be null

Octokit.Tests.Integration/Clients/PullRequestsClientTests.cs

@@ -59,6 +59,7 @@ public async Task CanGetForRepository()
 
         Assert.Equal(1, pullRequests.Count);
         Assert.Equal(result.Title, pullRequests[0].Title);
+        Assert.True(pullRequests[0].Id > 0);
     }
 
     [IntegrationTest]

Octokit/Models/Response/Issue.cs

@@ -38,7 +38,7 @@ public Issue(Uri url, Uri htmlUrl, Uri commentsUrl, Uri eventsUrl, int number, I
         }
 
         /// <summary>
-        /// The Id for this issue
+        /// The internal Id for this issue (not the issue number)
         /// </summary>
         public int Id { get; protected set; }
 

Octokit/Models/Response/PullRequest.cs

@@ -15,8 +15,9 @@ public PullRequest(int number)
             Number = number;
         }
 
-        public PullRequest(Uri url, Uri htmlUrl, Uri diffUrl, Uri patchUrl, Uri issueUrl, Uri statusesUrl, int number, ItemState state, string title, string body, DateTimeOffset createdAt, DateTimeOffset updatedAt, DateTimeOffset? closedAt, DateTimeOffset? mergedAt, GitReference head, GitReference @base, User user, User assignee, IReadOnlyList<User> assignees, bool? mergeable, User mergedBy, int comments, int commits, int additions, int deletions, int changedFiles, Milestone milestone, bool locked)
+        public PullRequest(long id, Uri url, Uri htmlUrl, Uri diffUrl, Uri patchUrl, Uri issueUrl, Uri statusesUrl, int number, ItemState state, string title, string body, DateTimeOffset createdAt, DateTimeOffset updatedAt, DateTimeOffset? closedAt, DateTimeOffset? mergedAt, GitReference head, GitReference @base, User user, User assignee, IReadOnlyList<User> assignees, bool? mergeable, User mergedBy, int comments, int commits, int additions, int deletions, int changedFiles, Milestone milestone, bool locked)
         {
+            Id = id;
             Url = url;
             HtmlUrl = htmlUrl;
             DiffUrl = diffUrl;
@@ -47,6 +48,11 @@ public PullRequest(Uri url, Uri htmlUrl, Uri diffUrl, Uri patchUrl, Uri issueUrl
             Locked = locked;
         }
 
+        /// <summary>
+        /// The internal Id for this pull request (not the pull request number)
+        /// </summary>
+        public long Id { get; protected set; }
+
         /// <summary>
         /// The URL for this pull request.
         /// </summary>