init: add -o, --origin to name manifest remote

The -o option permits the user to control the name of the manifest's
remote, which normally is hardcoded to be 'origin', but can differ
because we derive it at runtime from the configuration file.

Signed-off-by: Shawn O. Pearce <sop@google.com>
diff --git a/manifest_xml.py b/manifest_xml.py
index 45896be..d888653 100644
--- a/manifest_xml.py
+++ b/manifest_xml.py
@@ -189,7 +189,10 @@
   def _Load(self):
     if not self._loaded:
       m = self.manifestProject
-      b = m.GetBranch(m.CurrentBranch).merge
+      b = m.GetBranch(m.CurrentBranch)
+      if b.remote and b.remote.name:
+        m.remote.name = b.remote.name
+      b = b.merge
       if b is not None and b.startswith(R_HEADS):
         b = b[len(R_HEADS):]
       self.branch = b