dnet throws an "OSError: No error" exception when we want to get
the outgoing interface and the interface has no IP address.
This uncaught exception made Scapy exit.

When enumerating usable network interfaces we now only
try those that have an IP address, because the IP address
is needed anyway to construct the mapping between dnet
and pcap interface names.

This significantly improves Scapy's startup performance.

Some people have reported dnet interface names like "eth14"
on Windows.

The old batch file worked on Python 2.5 but lead to the
following error under Python 2.6:
c:\Python26\python.exe: scapy is a package and cannot be directly executed
New file should work under both versions.

Added RawVal object that ca be assigned to any packet field and will inserted as-is in the packet string

ex:
>>> a=IP(len=RawVal("####"))
>>> str(a)
'F\x00####\x00\x01\x00\x005\xb5\x00\x00\x7f\x00\x00\x01\x7f\x00\x00\x01\x00\x00'