fetch/pull doc: untangle meaning of bare <ref>

The documentation erroneously used the same wording for both fetch and
pull, stating that something will be merged even in git-fetch(1).

In addition, saying that "<ref> is equivalent to <ref>:" doesn't
really help anyone who still needs to read manpages.  Clarify what is
actually going on.

Signed-off-by: Thomas Rast <trast@inf.ethz.ch>
Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

Documentation/pull-fetch-param.txt

@@ -68,6 +68,11 @@ Some short-cut notations are also supported.
 +
 * `tag <tag>` means the same as `refs/tags/<tag>:refs/tags/<tag>`;
   it requests fetching everything up to the given tag.
-* A parameter <ref> without a colon is equivalent to
-  <ref>: when pulling/fetching, so it merges <ref> into the current
-  branch without storing the remote branch anywhere locally
+ifndef::git-pull[]
+* A parameter <ref> without a colon fetches that ref into FETCH_HEAD,
+endif::git-pull[]
+ifdef::git-pull[]
+* A parameter <ref> without a colon merges <ref> into the current
+  branch,
+endif::git-pull[]
+  while not storing the branch anywhere locally.