xentrace: make xentrace and xenmon work on Solaris and *BSD.

xentrace: make xentrace and xenmon work on Solaris and *BSD.
 - Use getopt() to get rid of argp dependency which does not exist
   on Solaris and *BSD. Done by Tariq Magdon-Ismail.
 - Minor modifications by me (Christoph) to make it also work on *BSD.
 - Tested on Linux by me (Christoph). No functional change on Linux.
 - Tariq ok'd BSD modifications for Solaris
 - Tariq ok'd submission by me :)

Signed-off-by: Tariq Magdon-Ismail <tariqmi@sun.com>
Signed-off-by: Christoph Egger <Christoph.Egger@amd.com>