Correct Repository.get_git_tree recursive use (#767)

The API docs for Repository.get_git_tree specify that the URL parameter
for fetching a tree recursively should be ?recursive=1, not a truthy
value. To not change the API we present, check if it is True before
setting it to 1. Change another callsite of Repository.get_git_tree to
specify recursive=False to make sure it doesn't appear in the query
string.

Fixes #560

github/Repository.py

@@ -1727,8 +1727,9 @@ class Repository(github.GithubObject.CompletableGithubObject):
         assert isinstance(sha, (str, unicode)), sha
         assert recursive is github.GithubObject.NotSet or isinstance(recursive, bool), recursive
         url_parameters = dict()
-        if recursive is not github.GithubObject.NotSet:
-            url_parameters["recursive"] = recursive
+        if recursive is not github.GithubObject.NotSet and recursive:
+            # GitHub API requires the recursive parameter be set to 1.
+            url_parameters["recursive"] = 1
         headers, data = self._requester.requestJsonAndCheck(
             "GET",
             self.url + "/git/trees/" + sha,

github/tests/ReplayData/Repository.testGetGitTreeWithRecursive.txt

@@ -2,7 +2,7 @@ https
 GET
 api.github.com
 None
-/repos/jacquev6/PyGithub/git/trees/f492784d8ca837779650d1fb406a1a3587a764ad?recursive=True
+/repos/jacquev6/PyGithub/git/trees/f492784d8ca837779650d1fb406a1a3587a764ad?recursive=1
 {'Authorization': 'Basic login_and_password_removed', 'User-Agent': 'PyGithub/Python'}
 None
 200

github/tests/Repository.py

@@ -267,7 +267,7 @@ class Repository(Framework.TestCase):
         self.assertEqual(tree.sha, "41cf8c178c636a018d537cb20daae09391efd70b")
 
     def testCreateGitTreeWithBaseTree(self):
-        base_tree = self.repo.get_git_tree("41cf8c178c636a018d537cb20daae09391efd70b")
+        base_tree = self.repo.get_git_tree("41cf8c178c636a018d537cb20daae09391efd70b", recursive=False)
         tree = self.repo.create_git_tree(
             [github.InputGitTreeElement(
                 "Barbaz.txt",