65c042d4 broke `remote update' without named group

[YONETANI Tomokazu <qhwt+git@les.ath.cx>]

Hello.
It seems that with 65c042d4 (and v1.6.6), git-remote update without
specifying a group on the command line ends up with the following error
message if you define remotes.default in the config file:
  $ git remote update
  fatal: 'default' does not appear to be a git repository
  fatal: The remote end hung up unexpectedly

The document still says that when you don't specify the named group,
remotes.default in the configuration will get used, so this should work
(and it used to work with v1.6.4).

After the commit 65c042d4, the commands are translated as follows:
  $ git remote update
  ==> git-fetch default		(with remotes.default defined)		NG
  ==> git-fetch --all		(without remotes.default defined)	OK

  $ git remote update default
  ==> git-fetch --multiple default					OK

So just adding "--multiple" in front of "default" in the first case
above should fix it.

Best regards,
YONETANI Tomokazu.