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Write a program, 'wordladder', which gets two arguments, which are
words of the same length, and which constructs and prints a "word
ladder" from the first word to the second word.

A word ladder from word AAA to word BBB is a sequence of dictionary
words such that:

1. the first word in the sequence is word AAA
2. each word in the sequence after the first differs from the previous
   word in exactly one letter position
3. the last word in the sequence is word BBB

For example, given the two words "love" and "hate", the program might
print the word ladder:

        love
        hove
        have
        hate

Or it might print:

        love
        lave
        have
        hate

It might also print a longer word ladder, such as

        love
        lore
        lobe
        robe
        role
        rose
        lose
        lost
        most
        mosh
        moth
        math
        hath
        hate

If the program is unable to find a word ladder, it should print an
appropriate error message to the standard error, and exit with a
failure status.

The program should also accept an optional third argument, which, if
specified, is the name of a dictionary file which contains the
permissible words.  If the third argument is omitted, the program
should use a default dictionary.

Sample word lists are available from
        [URL=http://perl.plover.com/qotw/words/]http://perl.plover.com/qotw/words/[/URL]