Add very numerous bug fixes and features, from Norse Corp.

* Fix some corner cases with greedy mode, where ports would be
  tracked inside httperf rather than the OS.  There were handfuls
  of corner cases where it'd either loop over an already-allocated
  port by the OS and chew 100% of cpu with no progress. Also, hit an
  already allocated port by the OS, skip/stop, but then the next lookup
  would hit that port again - it would never find a new port to open.

* Add kqueue support for FreeBSD. (No, not using libevent. Yet.)

* Add a periodic stats option, to print out 200/302 counts once
  every second.  This is to aid in automatic scripts looking to graph
  the progress being made.

* Add the ability to define multiple local client addresses, so
  requests can come from a much bigger pool of IP addresses.
  This allows for much more concurrency per process.)

* Add an explicit timeout on how long httperf can run - again, to aid
  in automated testing.

* Add an option to allow header contents to be loaded in from a file.

* Other fixes, mostly type related fixes, thanks to clang/llvm on
  FreeBSD-10.

We're using this in production at Norse to stress test out things,
upwards of 25,000 requests per second per httperf process.

This is a hold-over from using select() back in the past.
It now uses libevent, so it no longer (itself) cares about the size of
FD_SETSIZE.

Tidyups of this stuff will follow.