Fix 'Bugs 4, 5, and 6' which all use a similar fix but would have
conflicts over '#define BIGBUFSZ' if committed separately.
Format ("short explanation %s", string_argument), where the
explanation always has modest length but the string is potentially
up to 4*BUFSZ in length, into a 5*BUFSZ buffer. Then truncate the
result to at most BUFSZ-1 characters so that it can be safely passed
to interface-specific putstr() or raw_print().
Applies to pline(), raw_printf(), and config_error_add(). Also done
for impossible() although there's no evidence that its buffer could
be overflowed in a controlled manner.
Fix 'Bug 3' where too long SYMBOL=string in run-time config file could
overflow a local buffer and clobber the stack.
Valid value is only one character long after processing an 'escaped'
encoded character which can be at most 6 characters (plus terminator):
backslash M backslash and up three digits. If/when UTF8 gets added
the number of digits will increase. Use a truncated copy of the input
(substantially bigger than 6+1); ignore any excess.
Fix 'Bug 2' where too long MENUCOLOR=string in run-time config file
could overflow a local buffer and clobber the stack.
Theoretically a menu coloring regular expression could require a
bigger buffer but I don't think we need to try to support that.
255 characters minus the amount needed to specify color and/or
attributes should be ample.
