Add 'repo init --mirror' to download a complete forrest

The mirror option downloads a complete forrest (as described by the
manifest) and creates a replica of the remote repositories rather
than a client working directory.  This permits other clients to
sync off the mirror site.

A mirror can be positioned in a "DMZ", where the mirror executes
"repo sync" to obtain changes from the external upstream and
clients inside the protected zone operate off the mirror only,
and therefore do not require direct git:// access to the external
upstream repositories.

Signed-off-by: Shawn O. Pearce <sop@google.com>
diff --git a/repo b/repo
index 9f107a9..bfa4ca3 100755
--- a/repo
+++ b/repo
@@ -28,7 +28,7 @@
 del magic
 
 # increment this whenever we make important changes to this script
-VERSION = (1, 6)
+VERSION = (1, 7)
 
 # increment this if the MAINTAINER_KEYS block is modified
 KEYRING_VERSION = (1,0)
@@ -115,6 +115,9 @@
 group.add_option('-m', '--manifest-name',
                  dest='manifest_name',
                  help='initial manifest file', metavar='NAME.xml')
+group.add_option('--mirror',
+                 dest='mirror', action='store_true',
+                 help='mirror the forrest')
 
 # Tool
 group = init_optparse.add_option_group('Version options')