ptx default ignore file

[Eric Blake]

According to "info '(coreutils)Input processing in ptx'", if -i is not 
specified,
the file /usr/local/lib/eign is typically used.  However, looking at the source,
the default for -i is determined by the definition of DEFAULT_IGNORE_FILE,
which is not defined, nor mentioned anywhere outside of ptx.c.  Does it
still make sense to document a default file if we don't compile one in?

[Also, it appears that anon CVS is stuck again - the last publicly-visible
commit was on the 30th.]

-- 
Eric Blake