Documentation: @{-N} can refer to a commit

The @{-N} syntax always referred to the N-th last thing checked out,
which can be either a branch or a commit (for detached HEAD cases).
However, the documentation only mentioned branches.

Edit in a "/commit" in the appropriate places.

Reported-by: Kevin <ikke@ikke.info>
Signed-off-by: Thomas Rast <tr@thomasrast.ch>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

Documentation/git-checkout.txt

@@ -232,8 +232,8 @@ section of linkgit:git-add[1] to learn how to operate the `--patch` mode.
 	commit, your HEAD becomes "detached" and you are no longer on
 	any branch (see below for details).
 +
-As a special case, the `"@{-N}"` syntax for the N-th last branch
+As a special case, the `"@{-N}"` syntax for the N-th last branch/commit
-checks out the branch (instead of detaching).  You may also specify
+checks out branches (instead of detaching).  You may also specify
 `-` which is synonymous with `"@{-1}"`.
 +
 As a further special case, you may use `"A...B"` as a shortcut for the

Documentation/revisions.txt

@@ -88,7 +88,7 @@ some output processing may assume ref names in UTF-8.
   branch 'blabla' then '@\{1\}' means the same as 'blabla@\{1\}'.
 
 '@\{-<n>\}', e.g. '@\{-1\}'::
-  The construct '@\{-<n>\}' means the <n>th branch checked out
+  The construct '@\{-<n>\}' means the <n>th branch/commit checked out
   before the current one.
 
 '<branchname>@\{upstream\}', e.g. 'master@\{upstream\}', '@\{u\}'::