git-sh-setup: Fix scripts whose PWD is a symlink to a work-dir on OS X

On Mac OS X and possibly BSDs, /bin/pwd reads PWD from the environment if
available and shows the logical path by default rather than the physical
one.

Unset PWD before running /bin/pwd in both cd_to_toplevel and its test.

Still use the external /bin/pwd because in my Bash on Linux, the builtin
pwd prints the same result whether or not PWD is set.

Signed-off-by: Marcel M. Cary <marcel@oak.homeunix.org>
Tested-by: Wincent Colaiuta <win@wincent.com> (on Mac OS X 10.5.5)
Tested-by: Marcel Koeppen <git-dev@marzelpan.de> (on Mac OS X 10.5.6)
Signed-off-by: Junio C Hamano <gitster@pobox.com>

git-sh-setup.sh

@@ -96,7 +96,7 @@ cd_to_toplevel () {
 		..|../*|*/..|*/../*)
 			# Interpret $cdup relative to the physical, not logical, cwd.
 			# Probably /bin/pwd is more portable than passing -P to cd or pwd.
-			phys="$(/bin/pwd)/$cdup"
+			phys="$(unset PWD; /bin/pwd)/$cdup"
 			;;
 		*)
 			# There's no "..", so no need to make things absolute.

t/t2300-cd-to-toplevel.sh

@@ -10,12 +10,12 @@ test_cd_to_toplevel () {
 			cd '"'$1'"' &&
 			. git-sh-setup &&
 			cd_to_toplevel &&
-			[ "$(/bin/pwd)" = "$TOPLEVEL" ]
+			[ "$(unset PWD; /bin/pwd)" = "$TOPLEVEL" ]
 		)
 	'
 }
 
-TOPLEVEL="$(/bin/pwd)/repo"
+TOPLEVEL="$(unset PWD; /bin/pwd)/repo"
 mkdir -p repo/sub/dir
 mv .git repo/
 SUBDIRECTORY_OK=1