Introduce manifest format using git submodules

If a manifest top level directory contains '.gitmodules' we now
assume this is a git module format manifest and switch to using
that code, rather than the legacy XML based manifest.

At the same time, we move the bare repository for a project from
$TOP/.repo/projects/$REPO_PATH.git to be $REPO_NAME.git instead.
This makes it easier for us to later support a repo init from an
existing work tree, as we can more accurately predict the path of
the project's repository in the workspace.  It also means that the
$TOP/.repo/projects/ directory is layed out like a mirror would be.

Signed-off-by: Shawn O. Pearce <sop@google.com>
diff --git a/subcmds/init.py b/subcmds/init.py
index b5207fb..cdbbfdf 100644
--- a/subcmds/init.py
+++ b/subcmds/init.py
@@ -21,6 +21,7 @@
 from error import ManifestParseError
 from project import SyncBuffer
 from git_command import git_require, MIN_GIT_VERSION
+from manifest_submodule import SubmoduleManifest
 from manifest_xml import XmlManifest
 from subcmds.sync import _ReloadManifest
 
@@ -144,6 +145,14 @@
       print >>sys.stderr, 'fatal: cannot obtain manifest %s' % r.url
       sys.exit(1)
 
+    if is_new and SubmoduleManifest.IsBare(m):
+      new = self.GetManifest(reparse=True, type=SubmoduleManifest)
+      if m.gitdir != new.manifestProject.gitdir:
+        os.rename(m.gitdir, new.manifestProject.gitdir)
+        new = self.GetManifest(reparse=True, type=SubmoduleManifest)
+      m = new.manifestProject
+      self._ApplyOptions(opt, is_new)
+
     if not is_new:
       # Force the manifest to load if it exists, the old graph
       # may be needed inside of _ReloadManifest().