Only allow a version number to be read from "/etc/debian_version"

mysql-test/mysql-test-run.pl

@@ -1626,7 +1626,7 @@ sub environment_setup () {
   my $deb_version;
   if (  $opt_valgrind and -d $debug_libraries_path and
         (! -e '/etc/debian_version' or
-         ($deb_version= mtr_grab_file('/etc/debian_version')) == 0 or
+	 ($deb_version= mtr_grab_file('/etc/debian_version')) !~ /^[0-9]+\.[0-9]$/ or
          $deb_version > 3.1 ) )
   {
     push(@ld_library_paths, $debug_libraries_path);