configure's tar ustar test can fail on Solaris

[Mark Davies]

The grep on Solaris has difficulty with binary files so may not detect
the "ustar" in the output of tar during the configure test for tar 
speaking USTAR.  The below patch fixes by passing the output through
strings first.

--- m4/tar-ustar.m4.orig	Sun Jul  9 10:07:40 2006
+++ m4/tar-ustar.m4	Sun Jul  9 10:07:57 2006
@@ -27,7 +27,7 @@
      if test x$_mytar != x ; then
         AC_MSG_CHECKING([whether $_mytar speaks USTAR])
         echo hithere > conftest.txt
-        $_mytar -cf - conftest.txt | grep -q ustar
+        $_mytar -cf - conftest.txt | strings | grep -q ustar
         _tar_bad=$?
         rm conftest.txt
 
cheers
mark