noting backward incompatibility in b10-config.db

See http://bind10.isc.org/wiki/ChangeLogDetails

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Lines too long.

and mention it is planned for other systems.

introduced at entry "359" (which should have been 350).

- ChangeLog from master merged.
- dhcp4_srv cleanup (echo remnants removed, assignLease renamed)
- Pkt4::unpack() now is void and throws in case of problems