xenctx: Add command line option -D (--decode-as-ascii)

xenctx: Add command line option -D (--decode-as-ascii)

If specified, output ascii version of stack also.

This is not the default because the result exceeds 80 characters per line.

Here is an example:

Stack:
 ffffffff80048d19 0000000000200800 ffffffff803e7801 0000000000086800  .......... ......x>......h......
 0000000000000000 ffffffff80430720 ffffffff803e722f 80008e000010019c  ........ .C...../r>.............
 00000000ffffffff 0000000000000000 0000000000000000 0000000000200000  .......................... .....
 0000000000000000 0000000000000000                                    ................

Signed-off-by: Don Slutz <Don@CloudSwitch.com>
Acked-by: Ian Campbell <ian.campbell@citrix.com>