[3074] Add logging
[3074] Add logging
[3074] Add logging
[3074] Unsubscribe from earlier CC session first
[3191] Subnet4 now stores siaddr
[3191] Parser is now able to parse next-server parameter
[3186] Initial classes in DHCP user check hook library

Adds new source tree branch, bind10/src/hooks, for maintaining
custom hooks libraries.  Adds bare bones implementation of UserRegistry
for use in custom DHCP hooks library.
[3191] Unit-tests for siaddr configuration
[3191] User's Guide updated
[3186] Added support for loading user data from file

Added UserFile derivation of UserDataSource which allows the UserRegistry
to be populated from a JSON formatted file.
[3186] Fixed a couple of minor errors found on Fedora

Needed an include of stdint.h and to initialize the UserDataSource::open_flag_
in its constructor.
[3186] Implemented initial callouts for subnet_select

Added initial callout functions and ability to load the user_chk hooks library.
[3186] user_chk hook selects subnet4 based on user registry.

Interrim checkin. Subnet4 selection is working.
[3195] Initial support for unicast added.
[3195] Unicast log message bumped up to INFO.
[3195] Failed unicast bind no longer terminates control session.
[3195] Bugfix in activate IPv6 interfaces

 - exceptions are now more verbose
[3195] Socket selection for outgoing traffic improved
[3186] user_chk hook selects subnet6 based on user_registry

Interrim checkin. Subnet6 selection is working and user check outcome is
being written out to file, "/tmp/user_check_output.txt".
[3186] Adding logging to user_chk hook libraryU

Replaced couts with isc::log mechanisms in user_chk DHCP hook library.