Add manifest groups

Allows specifying a list of groups with a -g argument to repo init.
The groups act on a group= attribute specified on projects in the
manifest.
All projects are implicitly labelled with "default" unless they are
explicitly labelled "-default".
Prefixing a group with "-" removes matching projects from the list
of projects to sync.
If any non-inverted manifest groups are specified, the default label
is ignored.

Change-Id: I3a0dd7a93a8a1756205de1d03eee8c00906af0e5
Reviewed-on: https://gerrit-review.googlesource.com/34570
Reviewed-by: Shawn Pearce <sop@google.com>
Tested-by: Shawn Pearce <sop@google.com>
diff --git a/repo b/repo
index 1977d63..75fe9ec 100755
--- a/repo
+++ b/repo
@@ -28,7 +28,7 @@
 del magic
 
 # increment this whenever we make important changes to this script
-VERSION = (1, 14)
+VERSION = (1, 15)
 
 # increment this if the MAINTAINER_KEYS block is modified
 KEYRING_VERSION = (1,0)
@@ -125,6 +125,10 @@
 group.add_option('--depth', type='int', default=None,
                  dest='depth',
                  help='create a shallow clone with given depth; see git clone')
+group.add_option('-g', '--groups',
+                 dest='groups', default="",
+                 help='restrict manifest projects to ones with a specified group',
+                 metavar='GROUP')
 
 
 # Tool