[PATCH 1/4] contrib/diffall: change comment to reflect actual reason for 'cdup'

[Tim Henigan <tim.henigan@gmail.com>]

The comment from an earlier commit did not reflect the actual reason this
operation is needed.

Signed-off-by: Tim Henigan <tim.henigan@gmail.com>
---
 contrib/diffall/git-diffall |    4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/contrib/diffall/git-diffall b/contrib/diffall/git-diffall
index 9bbd27f..d706a6d 100755
--- a/contrib/diffall/git-diffall
+++ b/contrib/diffall/git-diffall
@@ -36,7 +36,9 @@ fi
 
 start_dir=$(pwd)
 
-# needed to access tar utility
+# All the file paths returned by the diff command are relative to the root
+# of the working copy. So if the script is called from a subdirectory, it
+# must switch to the root of working copy before trying to use those paths.
 cdup=$(git rev-parse --show-cdup) &&
 cd "$cdup" || {
 	echo >&2 "Cannot chdir to $cdup, the toplevel of the working tree"
-- 
1.7.10.rc0