[PATCH 0 of 1] Fix for issue 2970: abort clone when subrepository is inaccessible.

[Marc Simpson]

Hi all,

This is a patch against the current tip of the main repository
(ff3e93686306) to address issue 2970. A brief restatement of the
problem: Attempting to clone an 'hg serve' hosted repository
containing a subrepo yields traceback.

The provided fix will abort the clone when it encounters an
inaccessible subrepository; this means that a partial clone is left
behind. (I'm not sure what the best practice is here.)

Best,
Marc