Add AES-XEX tests cases

The test cases come from the XTS test vectors given by the CAVP initiative
from NIST (see [1]).
As mentioned in a previous commit, XEX is a simpler case of XTS.
Therefore, to construct the test_suite_aes.xex.data file, extraction of
the XEX-possible cases has been done on the given test vectors.
All of the extracted test vectors pass the tests on a Linux x86_64 machine.

[1] http://csrc.nist.gov/groups/STM/cavp/documents/aes/XTSTestVectors.zip
diff --git a/tests/CMakeLists.txt b/tests/CMakeLists.txt
index 653687b..4c938c6 100644
--- a/tests/CMakeLists.txt
+++ b/tests/CMakeLists.txt
@@ -48,6 +48,7 @@
 add_test_suite(aes aes.cbc)
 add_test_suite(aes aes.cfb)
 add_test_suite(aes aes.rest)
+add_test_suite(aes aes.xex)
 add_test_suite(arc4)
 add_test_suite(aria)
 add_test_suite(asn1write)