Update to 5.1.0

Changes from 5.0.6
* get_option_addr uses struct in_addr * instead of uint32_t *
  fixes a crash on sgimips/netbsd, thanks to Tim McIntosh
* Use ssize_t which is a signed int and test if read() returns -1
  fixes a crash on some embedded systems, thanks to David Wu
* Fix -f path/to/config
* -e, --env var=value for profile specific env vars
* Many issues resolved when running in test mode
* Don't print a (null) string when there is no NAK message
* Fix compile on NetBSD-4 (PR pkg/41719)
* Only allow hardware families we know by default (over-ridable)
* Fix persistent and timeout 0 options
* Fix parsing of escape code sequencies
* Don't bring up interfaces brought down when handling new interfaces
* Allow un-encapsulated vendor option
* Build system now uses configure script and not mk stubs

(roy)