bpo-27593: Get SCM build info from git instead of hg. (#446)

sys.version and the platform module python_build(),
python_branch(), and python_revision() functions now use
git information rather than hg when building from a repo.

Based on original patches by Brett Cannon and Steve Dower.

Lib/test/test_platform.py

@@ -67,12 +67,12 @@ class PlatformTest(unittest.TestCase):
 
     def setUp(self):
         self.save_version = sys.version
-        self.save_mercurial = sys._mercurial
+        self.save_git = sys._git
         self.save_platform = sys.platform
 
     def tearDown(self):
         sys.version = self.save_version
-        sys._mercurial = self.save_mercurial
+        sys._git = self.save_git
         sys.platform = self.save_platform
 
     def test_sys_version(self):
@@ -102,7 +102,7 @@ class PlatformTest(unittest.TestCase):
              ('CPython', '2.4.3', '', '', 'truncation', '', 'GCC')),
             ):
             # branch and revision are not "parsed", but fetched
-            # from sys._mercurial.  Ignore them
+            # from sys._git.  Ignore them
             (name, version, branch, revision, buildno, builddate, compiler) \
                    = platform._sys_version(input)
             self.assertEqual(
@@ -149,10 +149,10 @@ class PlatformTest(unittest.TestCase):
                 sys_versions.items():
             sys.version = version_tag
             if subversion is None:
-                if hasattr(sys, "_mercurial"):
-                    del sys._mercurial
+                if hasattr(sys, "_git"):
+                    del sys._git
             else:
-                sys._mercurial = subversion
+                sys._git = subversion
             if sys_platform is not None:
                 sys.platform = sys_platform
             self.assertEqual(platform.python_implementation(), info[0])