* src/ltlvisit/basicreduce.cc: Perform the following reductions:
(a U b) & (c W b) = (a & c) U b
(a W b) & (c W b) = (a & c) W b
(a R b) | (c M b) = (a | c) R b
(a M b) | (c M b) = (a | c) M b
* src/ltltest/reduccmp.test: Test them.