* src/ltlvisit/length.cc: Fix computation for ltl::multop
operator. "a&b&c" was reported with length 3, ignoring the
"&" operators, because of a typo.
* src/ltlvisit/length.hh: Fix description to correctly
reflect this change intended since 2010-01-22.
* src/ltltest/length.test, src/ltltest/length.cc: New files.
* src/ltltest/Makefile.am: Add them.
