Don't use the __attribute__((packed)) on most platforms.

It won't necessarily work with non-GCC-compatible compilers, so use it
only on GCC-compatible compilers.

Even with some GCC-compatible compilers (such as, err, umm, GCC), it
doesn't do the right thing on some platforms, e.g. 64-bit SPARC, where
the compiler generates code that assumes alignment even when using it.
The only platforms I know of where an unaligned big-endian load can be
done better than by loading bytes and shifting-and-ORing them together
are MIPS and possibly Alpha, so only do it there.
Fix a compiler warning.

It's not necessarily safe to do pre-increment or post-increment in an
argument to an EXTRACT_ macro.
Do our own isascii(), isprint(), isgraph(), and toascii().

We do *not* want the behavior of isprint() and isgraph() to be
locale-dependent - we want both of them to return "true" only for ASCII
characters.

We have to do our own isascii() and toascii() on non-UN*X systems
anyway, so let's just do all of them ourselves.
Use the new libpcap <pcap/nflog.h> for NFLOG definitions and declarations.

Use the header file for information about LINKTYPE_NFLOG files.

Don't build the NFLOG printer if we don't have that header file.

Fix some checks for pcap/XXX.h header files to look for
"tcpdump-stdinc.h" rather than <tcpdump-stdinc.h>, so that we don't fail
to find that header.
With -A and -AA, don't send CRs to the standard output.

They don't belong on the ends of lines on UN*X, and the standard I/O
library will give us one at the end of the line on Windows so they're
not needed there.  In the middle of a line, just print a ".".
Clean up the TLV processing loop.

We want to process TLVs until we run out of data, so make the main loop
condition "length > 0".  Break out of the loop if we see an
NFULA_PAYLOAD TLV.

Add in a bunch of length checks, and make those and existing length
checks report "[|nflog]".
Support -Q for setting the capture direction.

Also warn with -P that -Q should be used instead, as -P will be used in
the future for writing pcap-ng files (that's what the OS X tcpdump uses,
starting in Mountain Lion).