Use "ln -s" to link man pages by default.

Use AC_PROG_LN_S to determine whether "ln -s" works and, if not, whether
"ln" works and set LN_S appropriately for a link command, and use that
(as documented in the autoconf man page) to give man pages multiple
names.  (As the documentation says, to only way to make $(LN_S) work
regardless of how it's set is to execute it in the target directory.)
Check for malloc failing in pcap_ether_aton().

That also means that the lexical analyzer, which calls
pcap_ether_aton(), needs to check for pcap_ether_aton() failing.
Check for malloc failing in pcap_lib_version().

Yes, this means that on Windows and DOS you need to check whether
pcap_lib_version() returns NULL; otherwise, this just trades a crash in
pcap for a crash in the code calling it.
Support filtering filtering E1 SS7 traffic on MTP2 layer Annex A.

Originally written by Florent Drouin; applied to 1.3.0 by
dzejarczech@sourceforge.net.

Reviewed-By: Guy Harris <guy@alum.mit.edu>