subrepo: support Git being named "git.cmd" on Windows (issue3173) stable

subrepo: support Git being named "git.cmd" on Windows (issue3173)

Popen does not consider "foo.cmd" equivalent to "foo" on Windows.
Unfortunately, the default MSYS Git installation installs only "git.cmd" into
the path by default.  This patch probes for both possible names on Windows.

--- a/mercurial/subrepo.py	Tue Jun 12 09:28:55 2012 -0400
+++ b/mercurial/subrepo.py	Tue Jun 12 09:31:04 2012 -0400
@@ -850,7 +850,14 @@
         self._ensuregit()
 
     def _ensuregit(self):
-        out, err = self._gitnodir(['--version'])
+        try:
+            self._gitexecutable = 'git'
+            out, err = self._gitnodir(['--version'])
+        except OSError, e:
+            if e.errno != 2 or os.name != 'nt':
+                raise
+            self._gitexecutable = 'git.cmd'
+            out, err = self._gitnodir(['--version'])
         m = re.search(r'^git version (\d+)\.(\d+)\.(\d+)', out)
         if not m:
             self._ui.warn(_('cannot retrieve git version'))
@@ -883,8 +890,8 @@
         errpipe = None
         if self._ui.quiet:
             errpipe = open(os.devnull, 'w')
-        p = subprocess.Popen(['git'] + commands, bufsize=-1, cwd=cwd, env=env,
-                             close_fds=util.closefds,
+        p = subprocess.Popen([self._gitexecutable] + commands, bufsize=-1,
+                             cwd=cwd, env=env, close_fds=util.closefds,
                              stdout=subprocess.PIPE, stderr=errpipe)
         if stream:
             return p.stdout, None