Add support for .deb files which have control.tar.xz

[suihkulokki]

Fixes issue #395. Testcase .deb:s at: http://people.linaro.org/~riku.voipio/fix-obsbuild/

Before my patches:

528a3601f6d4707259c046c64ec637eb
$VAR1 = {
          'provides' => [],
          'source' => 'hello',
          'hdrmd5' => '528a3601f6d4707259c046c64ec637eb',
          'name' => 'hello',
          'requires' => [
                          'libc6 (>= 2.14)'
                        ]
        };

hxz.deb: control.tar.gz is not second ar entry

hxz.deb: control.tar.gz is not second ar entry
$VAR1 = undef;

And with patches:

528a3601f6d4707259c046c64ec637eb
$VAR1 = {
          'source' => 'hello',
          'requires' => [
                          'libc6 (>= 2.14)'
                        ],
          'provides' => [],
          'name' => 'hello',
          'hdrmd5' => '528a3601f6d4707259c046c64ec637eb'
        };

56be34240ac273298ec9e37bd61b26f2
$VAR1 = {
          'source' => 'hello',
          'hdrmd5' => '56be34240ac273298ec9e37bd61b26f2',
          'name' => 'hello',
          'requires' => [
                          'libc6 (>= 2.14)'
                        ],
          'provides' => []
        };

Unfortunately I have no knowledge how perl testsuite works, so I don't know howto integrate the above under tests.

[mlschroe]

Thanks!