Use git-update-ref and git-symbolic-ref in tests

This makes all tests pass on cygwin.

Signed-off-by: Johannes Schindelin <Johannes.Schindelin@gmx.de>
Signed-off-by: Junio C Hamano <junkio@cox.net>

t/t5000-tar-tree.sh

@@ -41,8 +41,8 @@ test_expect_success \
      find a -type l | xargs git-update-index --add &&
      treeid=`git-write-tree` &&
      echo $treeid >treeid &&
-     TZ=GMT GIT_COMMITTER_DATE="2005-05-27 22:00:00" \
+     git-update-ref HEAD $(TZ=GMT GIT_COMMITTER_DATE="2005-05-27 22:00:00" \
-     git-commit-tree $treeid </dev/null >.git/HEAD'
+     git-commit-tree $treeid </dev/null)'
 
 test_expect_success \
     'git-tar-tree' \
@@ -59,7 +59,7 @@ test_expect_success \
 test_expect_success \
     'git-get-tar-commit-id' \
     'git-get-tar-commit-id <b.tar >b.commitid &&
-     diff .git/HEAD b.commitid'
+     diff .git/$(git-symbolic-ref HEAD) b.commitid'
 
 test_expect_success \
     'extract tar archive' \

t/t6001-rev-list-merge-order.sh

@@ -108,7 +108,7 @@ save_tag h2 unique_commit g4 tree -p g2
 save_tag g3 unique_commit g5 tree -p g2
 save_tag g4 unique_commit g6 tree -p g3 -p h2
 
-tag l5 > .git/HEAD
+git-update-ref HEAD $(tag l5)
 
 test_expect_success 'rev-list has correct number of entries' 'git-rev-list HEAD | wc -l | tr -s " "' <<EOF
 19

t/t6002-rev-list-bisect.sh

@@ -58,7 +58,7 @@ on_committer_date "1971-08-16 00:00:15" save_tag a4 unique_commit a4 tree -p a3
 on_committer_date "1971-08-16 00:00:16" save_tag l3 unique_commit l3 tree -p a4
 on_committer_date "1971-08-16 00:00:17" save_tag l4 unique_commit l4 tree -p l3
 on_committer_date "1971-08-16 00:00:18" save_tag l5 unique_commit l5 tree -p l4
-tag l5 > .git/HEAD
+git-update-ref HEAD $(tag l5)
 
 
 #     E

t/t6003-rev-list-topo-order.sh

@@ -77,7 +77,7 @@ save_tag h2 unique_commit g4 tree -p g2
 save_tag g3 unique_commit g5 tree -p g2
 save_tag g4 unique_commit g6 tree -p g3 -p h2
 
-tag l5 > .git/HEAD
+git-update-ref HEAD $(tag l5)
 
 test_expect_success 'rev-list has correct number of entries' 'git-rev-list HEAD | wc -l | tr -s " "' <<EOF
 19