[2246] Interface detection code for BSD and Solaris

 - Contributed by David Carlier
 - Clean-up by tomek
[3210] CfgMgr now can store a flag for echoing v4 client-id
[3210] client-id echo in DHCPv4 server is now configurable
[3210] Docs updated.
[3210] Fixed trivial issues in the CfgMgr.

This commit includes trivial changes to the doxygen documentation and
make one variable const.
[3181] Fixed bug which caused wrong calculation of a timeout for receiving.
[3181] Added support for the new perfdhcp command line option: release-rate
[3181] Moved -f and -F perfdhcp parameters to a DHCPv6 only options.
[3181] Added common function to create DHCPv6 Release and Renew messages
[3181] Send Release messages if -F<release-rate> is specified.
[3181] Fixed error in perfdhcp doxygen documentation.
[3181] Reset the time stamp of the last sent release.
[3181] Added an exchange name for Release-Reply in perfdhcp StatsMgr.
[3181] Moved perfdhcp rate control logic to a new class.
[3181] Added a RateControl class omitted in the previous commit.
[3181] Fixed doxygen errors in perfdhcp.
[3181] Temporarily disable displaying orphan messages.
[3088] Initial implementation of d2::NameRemoveTransaction

Interrim check-in for 3088, which introduces the initial
implementation of d2:NameRemoveTransaction.  This class
implements the state model logic necessary for removing
DNS entries per RFC 4703.  The state model logic is
complete, what remains is the logic to build the actual
request messages.
[1824] Use CMSG_SPACE instead of CMSG_LEN to set msg_controllen.

Both macros should be accepted, but CMSG_LEN appears not to work on
OpenBSD.
[1824] More descriptive error strings if the sendmsg function fails.