Special handling for manifest group "default"

Change Details:
* Make "default" a special manifest group that matches any project that
  does not have the special project group "notdefault"
* Use "default" instead of "all,-notdefault" when user does not specify
  manifest group
* Expand -g option help to include example usage of manifest groups

Change Benefits:
* Allow a more intuitive and expressive manifest groups specification:
  * "default" instead of "all,-notdefault"
  * "default,foo" instead of "all,-notdefault,foo"
  * "default,-foo" instead of "all,-notdefault,-foo"
  * "foo,-default" which has no equivalent
* Default manifest groups behavior can be restored by the command
  'repo init -g default'. This is significantly more intuitive than the
  current equivalent command 'repo init -g all,-notdefault'.

Change-Id: I6d0673791d64a650110a917c248bcebb23b279d3

1 files changed, 1 insertions, 1 deletions

diff --git a/command.py b/command.py
index 96d7848f..43988520 100644
--- a/command.py
+++ b/command.py
@@ -136,7 +136,7 @@ class Command(object):
 
     groups = mp.config.GetString('manifest.groups')
     if not groups:
-      groups = 'all,-notdefault,platform-' + platform.system().lower()
+      groups = 'default,platform-' + platform.system().lower()
     groups = [x for x in re.split(r'[,\s]+', groups) if x]
 
     if not args: