t5000: integrate export-subst tests into regular tests

Instead of creating extra archives for testing substitutions, set the
attribute export-subst and overwrite the marked file with the expected
(expanded) content right between committing and archiving.  Thus
placeholder expansion based on the committed content is performed with
each archive creation and the comparison with the contents of directory
a yields the correct result.  We can then remove the special tests for
export-subst.

Signed-off-by: René Scharfe <rene.scharfe@lsrfire.ath.cx>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

Author: René Scharfe

t/t5000-tar-tree.sh

@@ -62,6 +62,12 @@ test_expect_success \
      git update-ref HEAD $(TZ=GMT GIT_COMMITTER_DATE="2005-05-27 22:00:00" \
      git commit-tree $treeid </dev/null)'
 
+test_expect_success 'setup export-subst' '
+	echo "substfile?" export-subst >>.git/info/attributes &&
+	git log --max-count=1 "--pretty=format:A${SUBSTFORMAT}O" HEAD \
+		>a/substfile1
+'
+
 test_expect_success \
     'create bare clone' \
     'git clone --bare . bare.git &&
@@ -148,38 +154,6 @@ test_expect_success \
     'validate file contents with prefix' \
     'diff -r a c/prefix/a'
 
-test_expect_success \
-    'create archives with substfiles' \
-    'cp .git/info/attributes .git/info/attributes.before &&
-     echo "substfile?" export-subst >>.git/info/attributes &&
-     git archive HEAD >f.tar &&
-     git archive --prefix=prefix/ HEAD >g.tar &&
-     mv .git/info/attributes.before .git/info/attributes'
-
-test_expect_success \
-    'extract substfiles' \
-    '(mkdir f && cd f && "$TAR" xf -) <f.tar'
-
-test_expect_success \
-     'validate substfile contents' \
-     'git log --max-count=1 "--pretty=format:A${SUBSTFORMAT}O" HEAD \
-      >f/a/substfile1.expected &&
-      test_cmp f/a/substfile1.expected f/a/substfile1 &&
-      test_cmp a/substfile2 f/a/substfile2
-'
-
-test_expect_success \
-    'extract substfiles from archive with prefix' \
-    '(mkdir g && cd g && "$TAR" xf -) <g.tar'
-
-test_expect_success \
-     'validate substfile contents from archive with prefix' \
-     'git log --max-count=1 "--pretty=format:A${SUBSTFORMAT}O" HEAD \
-      >g/prefix/a/substfile1.expected &&
-      test_cmp g/prefix/a/substfile1.expected g/prefix/a/substfile1 &&
-      test_cmp a/substfile2 g/prefix/a/substfile2
-'
-
 test_expect_success 'git archive with --output, override inferred format' '
 	git archive --format=tar --output=d4.zip HEAD &&
 	test_cmp b.tar d4.zip