u_intN_t is dead, long live uintN_t.

And, as we require at least autoconf 2.61, and as autoconf 2.61 and
later have AC_TYPE_UINTn_T and AC_TYPE_INTn_T macros, we use them to
define the uintN_t and intN_t macros if the system doesn't define them
for us.

This lets us get rid of bitypes.h as well.
More getting rid of old u_intN_t.
Some indentation cleanups from the previous checkin.
We still need u_intN_t.

Some libpcap headers use them, and even if we change libpcap to use
uintN_t, we don't require that tcpdump 4.x go with libpcap 1.x - we
allow people to install the latest tcpdump even if they have an older
libpcap and don't want to install a newer one.

However, we now define them in terms of the C99 uintN_t types, rather
than trying to guess what's appropriate; using unsigned long long for
u_int64_t meant that, on some platforms, u_int64_t didn't match
PRI[doux]64, and using unsigned long obviously won't work on ILP32
platforms.

Also, we already had calls to the autoconf macros for C99 types; get rid
of the ones we added.

Also also, clean up a comment in tcpdump-stdinc.h.
More fixes for uint8_t being shorter than u_int8_t.

Fix a typo while we're at it.
make NFLOG test case conditional

Not all libpcap copies have the support for NFLOG (added in 2013), thus
only run the test when tcpdump was compiled for it.