t9903: Don't fail when run from path accessed through symlink

When the git directory is accessed through a symlink like

  ln -s /tmp/git /tmp/git-symlink
  cd /tmp/git-symlink/t
  make -C .. && ./t9903-bash-prompt.sh

$TRASH_DIRECTORY is /tmp/git-symlink/t/trash directory.t9903-bash-prompt
and $(pwd -P) is /tmp/git/t/trash directory.t9903-bash-prompt.

When __gitdir looks up the path through 'git rev-parse --git-dir', it
will return paths similar to $(pwd -P). This behavior is already tested in
t9903 'gitdir - resulting path avoids symlinks'.

Signed-off-by: Torstein Hegge <hegge@resisty.net>
Reviewed-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

t/t9903-bash-prompt.sh

@@ -59,7 +59,7 @@ test_expect_success 'gitdir - .git directory in cwd' '
 '
 
 test_expect_success 'gitdir - .git directory in parent' '
-	echo "$TRASH_DIRECTORY/.git" > expected &&
+	echo "$(pwd -P)/.git" > expected &&
 	(
 		cd subdir/subsubdir &&
 		__gitdir > "$actual"
@@ -77,7 +77,7 @@ test_expect_success 'gitdir - cwd is a .git directory' '
 '
 
 test_expect_success 'gitdir - parent is a .git directory' '
-	echo "$TRASH_DIRECTORY/.git" > expected &&
+	echo "$(pwd -P)/.git" > expected &&
 	(
 		cd .git/refs/heads &&
 		__gitdir > "$actual"
@@ -115,7 +115,7 @@ test_expect_success 'gitdir - non-existing $GIT_DIR' '
 '
 
 test_expect_success 'gitdir - gitfile in cwd' '
-	echo "$TRASH_DIRECTORY/otherrepo/.git" > expected &&
+	echo "$(pwd -P)/otherrepo/.git" > expected &&
 	echo "gitdir: $TRASH_DIRECTORY/otherrepo/.git" > subdir/.git &&
 	test_when_finished "rm -f subdir/.git" &&
 	(
@@ -126,7 +126,7 @@ test_expect_success 'gitdir - gitfile in cwd' '
 '
 
 test_expect_success 'gitdir - gitfile in parent' '
-	echo "$TRASH_DIRECTORY/otherrepo/.git" > expected &&
+	echo "$(pwd -P)/otherrepo/.git" > expected &&
 	echo "gitdir: $TRASH_DIRECTORY/otherrepo/.git" > subdir/.git &&
 	test_when_finished "rm -f subdir/.git" &&
 	(
@@ -137,7 +137,7 @@ test_expect_success 'gitdir - gitfile in parent' '
 '
 
 test_expect_success SYMLINKS 'gitdir - resulting path avoids symlinks' '
-	echo "$TRASH_DIRECTORY/otherrepo/.git" > expected &&
+	echo "$(pwd -P)/otherrepo/.git" > expected &&
 	mkdir otherrepo/dir &&
 	test_when_finished "rm -rf otherrepo/dir" &&
 	ln -s otherrepo/dir link &&