Also adjust tests correcting the expected behaviour.

   Completes initial implmementation of example hooks libary, user_chk.

Removed reponse packet type check from IPv6 packet_snd callout.
Corrected text in user chk doxygen page.

Addressed review comments which were largely minor. Limited use of
extern C linkage to only the callout functions themselves. Added
a dox page describing the library.  Added namespace user_chk.

3207 was created quite some time ago, so master was
merged into it first.

The obsolete usage of AC_OUTPUT was actually causing config.status
to be executed multiple times, which is a big waste of time. Changed
to use the correct AC_CONFIG_FILES and AC_CONFIG_COMMANDS macros
instead.

Conflicts:
	src/bin/d2/d2_messages.mes

Fixed two missed minor cleanups from the initial review.

Changes are largely clean up and commentary.

Some files were using #include <full/path/to/header> syntax which is
not desirable as the directory may move about in the source tree, and
all of the files it was including are local to perfdhcp so they should
be using #include "filename.h".

Recent changes to the perfdhcp tool introduced a new breakage when
configuring with srcdir != objdir. These were introuced by the code
using #include <tests/tools/perfdhcp/SOME_FILE.h> but there were no
-I flags set to allow for including files from the top level.

Conflicts:
	ChangeLog
	doc/guide/bind10-guide.xml

 - flag => configuration parameter
 - echoClientId test uses ASSERTs rather than EXPECTs

Conflicts:
	ChangeLog

 - tests/methods descriptions improved
 - CfgMgrTest.echoClientId improved
 - Redundant checks removed from Dhcpv4SrvTest.discoverEchoClientId
 - BIND10 Guide clarified
 - ChangeLog added