Add 'echo-client-id' statment, so that RFC 6842 behaviour can be
turned off for those clients and networks that find it impossible to
move past RFC 2131. Modelled on the same statement in recent ISC
versions, though we default to 'on' (a.k.a. RFC 6842) rather that
'off' (a.k.a. RFC 2131).

Problems reported by Bastien Durel (Xerox Phaser 6022 printer) and
Bryan Vyhmeister (Hon Hai Precision router) via misc@. Thanks!

Add missing function prototypes. Mark kw_cmp() as static like all
its friends.

branches: 1.17.4;
Adjust some long lines.

Eliminate #include inside *.h files and include only needed headers in
each *.c file.

Inspired by mention of header silliness by Edgar Pettijohn and mmcc@
on tech@.

Tweak parsing so that hostnames starting with 0-9 are accepted.

Reported long ago by matthieu@. Also Jacob Berkman via the lists.

Tests and suggestions from Jacob and Matthieu.

Hoist common assignments out of a series of if/if-else statements
in get_token(). Simplifies code and shrinks future diff.

No intentional functional change.

Correct switch between current and previous line buffers when
encountering a carriage return in the input.

Found by jsg@ a long time ago in a respository far, far away.

Stop pretending we still support FDDI or token ring hardware types.

idea ok deraadt@ matthew@

Fix "\" escape handling in read_string().

Problem noted, fix tested and ok sthen@.

Echo back the Relay Agent Information option if present (RFC 3046).
Also add support for the "ipsec-tunnel" hardware type as described in
RFC 3456.

ok henning@ krw@ (but needs more testing from others)

remove one-lease-per-client parameter which was never implemented (it
doesn't do anything and is not documented); ok henning@

list must be sorted

cleanup keyword lookup for the lexer, and remove keywords not valid in
either dhclient or dhcpd context; tested by many

Missing 'break;' found by lint. 'blass' is not the same as 'class'!

ok moritz@ otto@

Fix buffer overflows in dhcpd and dhclient. Closes PR#4306.

ok henning@

avoid aliasing with libc functions; ok henning

more crap bites the dust

time_t and kill a few dumb defines

may the whacking begin