t5000, t5003: create directories for extracted files lazily

Create the directories b and c just before they are needed instead of
up front.  For t5003 it turns out we don't need them at all.  For t5000
it makes the coming modifications easier.

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

t/t5000-tar-tree.sh

@@ -32,7 +32,7 @@ SUBSTFORMAT=%H%n
 
 test_expect_success \
     'populate workdir' \
-    'mkdir a b c &&
+    'mkdir a &&
      echo simple textfile >a/a &&
      mkdir a/bin &&
      cp /bin/sh a/bin &&
@@ -126,7 +126,7 @@ test_expect_success \
 
 test_expect_success \
     'extract tar archive' \
-    '(cd b && "$TAR" xf -) <b.tar'
+    '(mkdir b && cd b && "$TAR" xf -) <b.tar'
 
 test_expect_success \
     'validate filenames' \
@@ -143,7 +143,7 @@ test_expect_success \
 
 test_expect_success \
     'extract tar archive with prefix' \
-    '(cd c && "$TAR" xf -) <c.tar'
+    '(mkdir c && cd c && "$TAR" xf -) <c.tar'
 
 test_expect_success \
     'validate filenames with prefix' \

t/t5003-archive-zip.sh

@@ -37,7 +37,7 @@ check_zip() {
 
 test_expect_success \
     'populate workdir' \
-    'mkdir a b c &&
+    'mkdir a &&
      echo simple textfile >a/a &&
      mkdir a/bin &&
      cp /bin/sh a/bin &&