Feature/1054 msdhcp cache options 1172 msdhcp handles leases

Hi Ohad,
  I did find time to merge these two requests down onto the development branch!

  I have no explicit test code for this patch but it has been working in IFX for 8 months

  Thinking again about the problems that you raised with file locking and concurrency I no longer think that these issues could occur. The Native MS DHCP client always runs using the embedded Webrick server and this is not a threaded application. I have left the file locking in as it does not appear to cause a problem.