fetch doc: on pulling multiple refspecs

Replace desription of old-style "Pull:" lines in remotes/
configuration with modern remote.*.fetch variables.

As this note applies only to "git pull", enable it only
in git-pull manual page.

Signed-off-by: Junio C Hamano <gitster@pobox.com>
fetch doc: update refspec format description

The text made it sound as if the leading plus is the only thing that
is optional, and forgot that <lhs> is the same as <lhs>:, i.e. fetch
it and do not store anywhere.

Signed-off-by: Junio C Hamano <gitster@pobox.com>
fetch doc: remove "short-cut" section

It is misleading to mention that <ref> that does not store is to
fetch the ref into FETCH_HEAD, because a refspec that does store is
also to fetch the LHS into FETCH_HEAD.  It is doubly misleading to
list it as part of "short-cut".  <ref> stands for a refspec that has
it on the LHS with a colon and an empty RHS, and that definition
should be given at the beginning of the entry where the format is
defined.

Tentatively remove this misleading description, which leaves the
`tag <tag>` as the only true short-hand, so move it at the beginning
of the entry.

Signed-off-by: Junio C Hamano <gitster@pobox.com>
fetch doc: add a section on configured remote-tracking branches

To resurrect a misleading mention removed in the previous step,
add a section to explain how the remote-tracking configuration
interacts with the refspecs given as the command-line arguments.

Signed-off-by: Junio C Hamano <gitster@pobox.com>
fetch: allow explicit --refmap to override configuration

Since the introduction of opportunisitic updates of remote-tracking
branches, started at around f2690487 (fetch: opportunistically
update tracking refs, 2013-05-11) with a few updates in v1.8.4 era,
the remote.*.fetch configuration always kicks in even when a refspec
to specify what to fetch is given on the command line, and there is
no way to disable or override it per-invocation.

Teach the command to pay attention to the --refmap=<lhs>:<rhs>
command-line options that can be used to override the use of
configured remote.*.fetch as the refmap.

Signed-off-by: Junio C Hamano <gitster@pobox.com>
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