display-error segmentation fault

[Neil Jerram]

This is with a current CVS Guile (on a GNU/Linux system).

address@hidden neil]$ guile
guile> (display-error #f #f #f #f #f #f)
Segmentation fault (core dumped)
address@hidden neil]$ 

The problem arises because scm_display_error does not check that its
port argument actually is a port.  I'm not sure what the best fix is,
since it isn't clear -- owing to lack of a docstring -- to what extent
scm_display_error is really supposed to be a public procedure.

(gdb) run            
Starting program: /usr/local/bin/guile 
guile> (display-error #f #f #f #f #f #f)

Program received signal SIGSEGV, Segmentation fault.
scm_lfwrite (ptr=0x4008bc60 "ERROR", size=5, port=8564) at ports.c:926
926       scm_port *pt = SCM_PTAB_ENTRY (port);
(gdb) bt
#0  scm_lfwrite (ptr=0x4008bc60 "ERROR", size=5, port=8564) at ports.c:926
#1  0x4005fcf0 in scm_puts (s=0x4008bc60 "ERROR", port=8564) at ports.c:920
#2  0x4002ed10 in display_header (source=8564, port=8564) at backtrace.c:105
#3  0x4002f06d in display_error_body (a=0xbfffe818) at backtrace.c:194
...

Regards,
        Neil