* Fix IA_PD length error

I tested this and noticed wireshark wasn't parsing the message correctly. Turns out the length is wrong.

* Update regression.uts

Fix test for DHCP6OptIA_PD

* Update length of DHCP6OptIA_PD in test.

This PR makes it possible to check if several flags are all set, by
writting, for example, `if pkt[TCP].flags.SA:`.

It only works for single letter flags (e.g., will work for TCP().flags
but not for IP().flags), and only when getting a value.

Thanks @guedou for suggesting that.

It is now possible to write `pkt[TCP].flags.S = True`.

This makes it possible to write `if pkt[TCP].flags.S: [...]`.

A new test that triggers the bug (with ARPSourceMACField) has been added.

Fix IPv6 support on Windows

  - LLTDAttribute() produces a Raw instance (or crashes, when
    conf.debug_dissector is set).

  - str(LLTDAttribute(type=18)) crashes.

Thanks @gpotter2

Pypy won't run crypto tests on Travis CI because the cryptography
module cannot be installed with the Pypy version used.

See
  - https://github.com/pyca/cryptography/issues/2968 (discussion)
  - https://github.com/pyca/cryptography/issues/1141 (older)

Change the cryptographic library used in the following layers:
 * IPSec
 * TLS
 * Dot11

Notes:
 * Fix the WEP key in regression.uts: Should be a 40 bits key (5 ASCII)
   and 24 bits nonce for 64 bits WEP. The key was 8 ASCII => 88 bits
   in total
 * AES-GCM and AES-CMAC algorithms are now native in cryptography: add
   tests in ipsec.uts
 * cryptography only supports Python 2.6+
 * Fix the docstring for the pad method

Removed:
 * MD2 and MD4 hash algorithms for RSA in tls/crypto/pkcs1.py
 * AES-XCBC-96 not supported by cryptography.

Signed-off-by: Thomas Faivre <thomas.faivre@6wind.com>

Signed-off-by: Thomas Faivre <thomas.faivre@6wind.com>

I had not tested it last time... 
When running  `python`, the first parameter is the file. So here all the arguments were passed as the file name...

One can now use tcpdump or tshark to dissect packets from
Scapy. This can help, for example, to check Scapy's dissectors