Hello,

This patch to bigcore.exp addresses a few 64-bit problems:

- core file exceeding file system's file size limit

On a 64-bit system, the coredump can exceed the file-system's max 
file-size leading to a truncated corefile (the ia64 rhel3 system I was 
testing on maxed at 1x10^9 bytes / [us] 1 terabyte).  This patch 
modifies bigcore.c so that it sniffs out the file-size limit by probing 
for how far a seek will go, caping things at that limit.

- use 64-bit off_t if available

i386 GNU/Linux has a 64-bit off_t (off64_t).  This patch tries to use 
that to compute the file-size limit, if it is available

- assume things work when dejagnu / tcl screws up the file size

This restores (and better comments) an edge case I accidently changed 
with my last patch - it modifies bigcore.exp so that when dejagn/tcl 
botch the file size computation it's assumed things will work. 
Otherwize the test is incorrectly aborted on 32-bit systems, with a 
broken dejagnu/tcl, that do support large corefiles.

Test on i386, ia64 and amd64 rhel3 systems which all pass.

ok?
Andrew