Support <remove-project name="X"> in manifest to remove/replace X

The manifest files now permit removing a project so the user can
either keep it out of their client, or replace it with a different
project using an entirely different configuration.

Signed-off-by: Shawn O. Pearce <sop@google.com>

manifest.py

@@ -137,6 +137,16 @@ class Manifest(object):
             "no <manifest> in %s" % \
             self.manifestFile
 
+    for node in config.childNodes:
+      if node.nodeName == 'remove-project':
+        name = self._reqatt(node, 'name')
+        try:
+          del self._projects[name]
+        except KeyError:
+          raise ManifestParseError, \
+                'project %s not found' % \
+                (name)
+
     for node in config.childNodes:
       if node.nodeName == 'remote':
         remote = self._ParseRemote(node)