manual: Fix example finding commits referencing given content.

If I'm handed a file, then it typically lives outside the
working directory.  git-log only operates on in-tree files,
so the first 'filename' should be an in-tree one, or it should
look at all files.  This patch does the latter, so it would
also find renamed files.  However, it is also slower.

Signed-off-by: Lars Hjemli <hjemli@gmail.com>
Signed-off-by: Shawn O. Pearce <spearce@spearce.org>

Documentation/user-manual.txt

@@ -926,7 +926,7 @@ file such that it contained the given content either before or after the
 commit.  You can find out with this:
 
 -------------------------------------------------
-$  git log --raw --abbrev=40 --pretty=oneline -- filename |
+$  git log --raw --abbrev=40 --pretty=oneline |
 	grep -B 1 `git hash-object filename`
 -------------------------------------------------