butc: convert butc/dump.c to safer string handling

butc: convert butc/dump.c to safer string handling

Convert butc/dump.c to safer string handling functions to avoid buffer
overflows.

Reviewed-on: https://gerrit.openafs.org/12922
Reviewed-by: Benjamin Kaduk <kaduk@mit.edu>
Tested-by: BuildBot <buildbot@rampaginggeek.com>
(cherry picked from commit 70b7f743550a8ce02292a12c4188deaf85b1a533)

Change-Id: I7a062663b5ac2ab0000fe176c7bfdf3896cfb782
Reviewed-on: https://gerrit.openafs.org/13098
Reviewed-by: Benjamin Kaduk <kaduk@mit.edu>
Tested-by: BuildBot <buildbot@rampaginggeek.com>