Merge branch 'sg/clone-refspec-from-command-line-config' into jch

Merge branch 'sg/clone-refspec-from-command-line-config' into jch

"git clone -c var=val" is a way to set configuration variables in
the resulting repository, but it is more useful to also make these
variables take effect while the initial clone is happening,
e.g. these configuration variables could be fetch refspecs.

* sg/clone-refspec-from-command-line-config:
  Documentation/clone: document ignored configuration variables
  clone: respect additional configured fetch refspecs during initial fetch