* src/ltlvisit/length.hh (length_boolone): New function.
* src/ltlvisit/length.cc (length_boolone): Implement it using...
(length_boolone_visitor): ... this new visitor.
* src/ltltest/randltl.cc: Use length_boolone() to check the result
of the random generator, and ignore any formula larger (in
length()) than opt_f.  This fix a bug where the random formula
generator would sometime produce formula larger than requested,
because of the trivial rewriting of {f}[]->e as e|!f.
* src/ltltest/length.cc: Add option -b to call length_boolone().
* src/ltltest/length.test: Test length_boolone().