README got renamed to README.ad.
That's README.md, not README.ad.
Not all compilers that can be used support C++/C99-style comments.

Use #if 0/#endif, rather than a // comment, to keep a line of code from
being compiled.
No C++/C99-style comments; not all C compilers necessarily support them.
Clean up handling of -g and -O flags.

AC_PROG_CC adds -g and -O2 to CFLAGS if you're using GCC; don't bother
adding either of them, or -O, ourselves if we're using GCC.

Add -O for all non-GCC compilers.
Note that clang, for example, is considered "gcc" by autoconf.
We require autoconf 2.61 in configure.in; that suffices.

Don't say "we require 2.50" in various macros.
With .devel, add -g3 for MIPS C and DEC C.

Lifted from the libpcap configure script, which adds -g even without
.devel, presumably so that programs linked with libpcap can get
debugging symbols.

Those compilers are for dead OSes (IRIX, Tru64 UNIX); we should probably
do whatever voodoo is needed to get Sun^WOracle C, IBM's C compiler for
AIX, and HP C to build optimized with debug symbols.
We no longer use the GCC version, so don't fetch it.

Fix some indentation while we're at it.
Update a comment for the previous commit.
Explain why we set -xansi -signed for MIPS C.
Babel: improve printing of time intervals

All Babel intervals are encoded in centiseconds and must not be 0. In an
Update TLV the interval value 0xFFFF means infinity (RFC6126 Section
4.4.9). Update the test cases.
adopt MacOS deprecation workaround from FreeRADIUS

A MacOS build of tcpdump used to produce deprecation warnings on OpenSSL
function calls. Alan DeKok explained that this is the effect of Apple's
modifications to OpenSSL and that the very same problem has already been
solved in FreeRADIUS server source code with pre-processor macros.

Copy the macros into tcpdump header file and make use of them around the
functions that call OpenSSL functions.