lib/debug: retain full string in state.prog_name global

lib/debug: retain full string in state.prog_name global

setup_logging() retains a global pointer to the provided const string in
state.prog_name, which is later used in the debug_backend->reload()
callback.
Some setup_logging() callers, such as popt_common_callback(),
incorrectly assume that a dynamic buffer is safe to provide as a
prog_name parameter. Fix this by copying the entire string in
setup_logging().

Signed-off-by: David Disseldorp <ddiss@samba.org>
Reviewed-by: Andreas Schneider <asn@samba.org>