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>
