This patch aids the quick diagnosis of stack overflow bugs.
In the debug build when showing a stack trace, show stack limits
and stack frame addresses.  This results in the follow
appearance:

     (XEN) Stack base:ffff830000234000 limit:ffff830000233000
     (XEN) Xen call trace:
     (XEN)    ffff830000233c28[<ffff830000144fe4>] put_page_type+0xf8/0x455
     (XEN)    ffff830000233c48[<ffff830000140d0a>] 
put_page_and_type+0x15/0x20
     (XEN)    ffff830000233c88[<ffff830000142271>] 
put_page_from_l1e+0x12a/0x1ad
     (XEN)    ffff830000233cf8[<ffff83000014b7d9>] revalidate_l1+0x18f/0x1a7
     (XEN)    ffff830000233d88[<ffff83000014ba93>] ptwr_flush+0x2a2/0x4fb
     (XEN)    ffff830000233da8[<ffff83000014cd86>] 
cleanup_writable_pagetable+0x68/0x88
     (XEN)    ffff830000233f08[<ffff8300001469cf>] do_mmuext_op+0xd4/0xaf5
     (XEN)    00007cffffdcc0b7[<ffff8300001ca45d>] syscall_enter+0xad/0x107

Signed-off-by: Robert S. Phillips (rphillips@virtualiron.com)